Replying to an email inline rather than at the top marks you out as of a certain generation. Using text emojis rather than finding the graphical emoji does too.
Everyone needs to relax about AI generation anyway (did you learn something useful or not? If you did, does it matter if it was AI generated as a site?), but saying "this is what people under 30 frequently do, so it must be fake", is just this weird vibe spreading everywhere I don't get at all.