Where did the blank user guy go?!

This user with a blank username sent me a friend request and I was like, "Oh, cool!! One of those glitched accounts!! :3" and I accepted the request and then I saw that they had a bulletin and it was a bo burnham reference, and I was about to comment, but I left to go look up the lyrics to make sure I got  the response right, and when I clicked the back button of my browser to make a reply instead of a new comment, it was gone. :O

They're not on my friends list, and there's no trace of them in my notifications or friend requests. TwT

Their profile shows a 404 as well as the blog entry I was just looking at.

What happened? Did they get banned?! o_0