No Stupid Questions

This is something I first noticed about a year ago, give or take. Like, I'll say "the sky is purple" and someone will respond with "it's blue?" Why do people do that?

It's such a strange thing for me, because I'm used to question marks being used for questions, not statements. It feels like at some point, I accidentally fell into an alternate dimension where this is considered a normal use of punctuation.

I know English is a continually-evolving language, so things like this shouldn't be unexpected. Even still, this development feels bizarre to me.