I think it goes even beyond that. Online you can get a lot more socioeconomic, age-related mixing than IRL. On some websites there is a large contingent of actual children/college students who have never worked or don't understand certain social norms due to inexperience. Or, if you live in a bubble of highly paid professionals like many on this site (honestly, including me), you can be completely shocked seeing how the working class people you see but don't actively converse with (beyond pleasantries) think.
Also, on pseudonymous sites, you may not even be able to know this at a glance. Sometimes on reddit I have been baffled at the replies I've received, until I realized it was coming from a child, or an older conservative person living on disability.
I found some old posts of mine from when I was 15. If anyone ever finds them I will have to kill them.
It's not that I was mean or nasty, or pushing any boundaries – I was never like that – I was just ... 15.
Also turns out what people meant with "your English is very good" was "your English is very good for a 15 years old non-native speaker", and not "your English is very good".
Also, on pseudonymous sites, you may not even be able to know this at a glance. Sometimes on reddit I have been baffled at the replies I've received, until I realized it was coming from a child, or an older conservative person living on disability.