He's not the first one to notice the fire. That honor goes to his niece, who quite eagerly tells mommy about what she's found.
He is the first one to realize what it means, that this has escalated past petty feuds and into something more dangerous, and this kind of insult can't be allowed to stand- Talia seems more focused on getting them out, which he concedes is important.
The fire doesn't seem to care about their priorities. At least it hasn't reached the house yet.