Usernames are per-instance, though. So there could be a toofpic on another instance. I'd also add that, somewhat-annoyingly, at least on kbin, dunno about lemmy, the interface does not go out of its way to make which instance a user is on particularly clear. You have to click on their username and check. I am pretty sure that they are gonna have to change that soon, because otherwise, someone is just going to go around impersonating other people.
The current events at Reddit are the output of a corporation with no understanding how how to run a community driven site, and way too much financial desperation to take several steps back and learn it.
Whether the wave recedes and we scramble to repair our sandcastles, the tide is rising.