This looks like an unusually large Sphere.
Actually, it kind of looks like a planet.
Actually, it kind of looks like a familiar planet.
Also, once he gets clear of the giant crater where the complex housing the portal used to be, no one is shooting at him and nothing is blowing up. There are no more portals in sight.
"I found a planet. I found a real planet. I found the planet humans come from in my world. You don't have weird physics, you just have a weird magic system which allows pocket dimensions with weird physics. This planet looks perfectly normal if somewhat the worse for wear."
"Yep. And it's overrun by aliens. I will... wander around watching bits of the Earth self-destruct, I guess."
And Cam flies around, looking for aliens, possibly evacuating in something he'd like to get a tracking device on.
Come out come out wherever you are, aliens.
Cam lands.
Cam wonders vaguely how his program figured out "befoul", decides this is really not the time to go look at its inference backchain, and fumbles around with his vocabulary until he has his best approximation of "talk to me so I can talk to you".
Can he say 'I do not intend to kill you unless -'. Or 'you can live if you cooperate'. Or something.
Sentences such as the following begin to come clear:
"The others will destroy us!"
"They will destroy the planet!"
"We are befouled already!"
"I am frightened!"
"We are unclean!"
"I don't want to die!"
"I don't want you to die," Cam asserts through his translator. He is pretty sure the promises police will not come after him for not incorporating the conditional.
"I want you to talk." He pats his computer. "This can talk to me and it can talk to you. Talk to me."
It tentatively peers out of the building where it and the others are cowering.
"Terrifying filth creature, I am [untranslated phrase, probably a name]. [More untranslated speech]. Please do not kill us. We don't know what you want. We are very afraid."