FPS mean 'First Person Shooter'.

So technically, no, Fortnite is not a FPS but a TPS, Third-person shooter. And I don't see any problems letting kids play it. Sure it has guns, but no blood, swearing or any kind of sexual content. It's very kid-friendly in it's presentation.

you're close, part of the joke is that as you said "but Lego and Fortnite are (stereotypically) kid and/or autism interests."

but what it's really doing is jokingly stating that the lego star wars games are games for intellectuals. Lego Star Wars has been jokingly celebrated for a while on reddit as the true chad/patrician video game series and this is just another case of that joke being used