I found a user named notch on Arqade and I think it might be a fake. But it got me thinking: are there any users on this site that are a part of Mojang studios?
Are there any users from Mojang on Arqade?
Likely not, but we won't know unless they announce themselves in an answer, comment, or on their profile page. We have had developers of other games answer questions in the past, so it's not out of the question.
As for the 'notch' user - I doubt they are the actual Notch from Mojang. It's likely they are just a regular person that took on that name. Note that usernames here aren't unique - anyone can choose any username (except for some 'rude' names or other violations of the Code of Conduct etc).
So there may very well be users here that work at Mojang, but we would have no way to tell unless they made it public here.