Does she want a physics lesson because that's how you get a physics lesson.

She absolutely wants a physics lesson. She asks a dozen follow-up questions and says "oh wow" a lot and clearly thinks Cam and/or rocketry is the coolest thing since sliced bread.

Adorable. He will send her off with a physics book once he has a good idea of her level of understanding and interest.

She has the interest of someone who really loves science and the understanding level of someone whose last science class was years ago. She thanks him and skips off to show all her friends the textbook.

A week after Gringott's said they would get back to him in three business days, Cam gets an owl requesting a meeting as soon as possible. It's signed by the goblins' deputy ambassador to the Ministry of Magic.

Goodness. He can hop over via the stupid fireplace-based transit method rather than suffuse Britain with more clouds than it has already and pop up quite promptly.

This time the cart-ride is much longer, going at least twice as deep by a route so twisty it's practically impossible to tell which direction they've gone on net other than "down". The cart arrives at a little underground train station shared by similar carts and larger, more nicely-appointed ones. From there Cam is shown down a series of increasingly fancy corridors until he reaches an office that would be, if not at home in a Manhattan skyscraper, at least among equals. Everything is shiny, from the walls (marble) to the furniture (mahogany) to the goblin behind the desk (wearing red silk robes with moving silver embroidery). His escort introduces him to Deputy Ambassador Rangvald and leaves.

"So it seems you can create material that does not disappear or revert," he says without preamble. 

"Yes, like I said."

"What limits does this ability have? Is it learnable by any wizard, or restricted to a subset?"

"I'm not a wizard," Cam says.

"Are you a different variety of human, or a different species? How many of you are there? Is it heritable?"

"I used to be a human but now I'm a different species, billions, no."

"Billions? That seems highly unlikely."

"I mean, they don't live around here," he replies blandly.

"Does anyone other than you currently have the ability to dump gold into the economy of this planet."

"Not yet."

Deputy Ambassador Rangvald is not having the best day. "Would you care to explain."

"Well, I got here, and others could too, and on the whole it might be good if they did since it's easier to end material scarcity that way, but I can tell you about the monetary arrangements that work where this is already common."

"Please do!"

So Cam can explain about how he can make arbitrary things and this dooms all physical currency but with sufficiently attended-to cryptography various digital systems may remain alive and well, and you could probably substitute some suitable magical signature deal, and also daeva are okay but not as good as wizards at disguising themselves so if you recognize someone you can figure with as much confidence as you normally have that they are them, blah blah blockchain blah blah retina scans blah blah when there are this many demons around you can have them verify things on your end as-needed.

The Deputy Ambassador is relieved that Cam understands the importance of not destroying the economy but disconcerted by the sheer number of daeva. He asks a bunch of questions about privacy laws and intellectual property rights and contract dispute resolution, and calls in another, less elaborately dressed goblin who asks some extremely technical questions about the crypto and the blockchain.

Cam can answer questions and supplement as necessary with written materials.

His ability to conjure information he doesn't know about leads to some sidelong glances and muttering in Gobbledegook and then even more questions about data encryption.

"The state of the art in demon-proof encryption is the chip-locked computer. I have one myself. They can be installed safely - by demons, or less safely by conventional surgery - in humans. They use the habits of a person's brain to encode data and have yet to be hacked. I don't know how hard it would be to adapt them to non-human non-daeva persons."

This calls for the summoning of another subject matter expert to discuss whether this can be replicated by magic, because brain surgery designed for humans sounds like a terrible idea. Maybe you could do something like a simplified, stripped-down Pensieve with a tablet-and-stylus form factor? Communication with anyone who isn't in the same room is going to be the tricky bit. Can Cam's abilities intercept, for example, a Muggle telegraph?

"It depends. If it's written at either end, we can get that. If it's transmitted electrically by people who speak it out loud to translate, or it's semaphore or something, we can get it, but it's substantially harder, because we have to get the state of the transmission at each point in the relevant timespan and decipher it from there."