Yeah, right. A few months back in 2021 I was asked how to "make an app on the phone". Not FOR a phone, ON a phone, the complete development only using a phone. WTF?
And no, it wasn't a 12 year old kid, it was a 21 year old guy with a Bachelor of science degree.
You jest, but it's possible. There is an Android IDE that includes a compiler that runs on Android.
https://play.google.com/store/apps/details?id=com.aide.ui&hl...
But in this case it's 99% more likely that the person asking didn't have these in mind, but just misunderstood what it takes to make a regular mobile app and though it obvious that regular mobile app development happens on the phones themselves.
So they were correct by accident, and only because there are some niche environments very few actual apps - and no major one - were ever made on. So it's like being correct that there are aligators in Australia, but not because normally there would be as local fauna (which is what you had in mind, confusing them with crocodiles), but because it happened that some actual aligators escaped from some zoo and procreated in the wild outback.