I signed up maybe a month and half ago, published a question here and set a customized profile name. Now I return to find my username changed to this. Only the profile pic that I uploaded then stays as only proof this profile is somehow connected to me. Now what about the username?
The only name history I can see for your account is on the 15th of February. It looks like you changed your name and then 4 minutes later reset it. The events below are in reverse chronological order so the lower one actually happened earlier.
The times of the two name change events are
2018-02-15 18:42:49Z for the change to
2018-02-15 18:46:07Z for the reset.
I cannot see anything to suggest this was done by anyone but yourself.
Maybe you pressed a back button, ended up loading an old version of the page, and then clicked save and thus resaved a cached version.
Clicking the back button and then saving a cached copy of your profile actually seems most likely. Especially when combined with your profile picture history, the two name change events also coincide with profile picture changes.
It looks a lot like you changed your name then clicked back so you could change your profile picture. In doing so your browser loaded an outdated copy of your profile page with your old display name, and from that outdated page you changed your profile picture. When you clicked save the page had your old username and overwrote the name change you made only minutes earlier.
No mod was involved in editing your profile. Moderator changes or access to user profile information would have been logged, but nothing is in your history except a logged-in profile owner (presumably you) changing their profile name and picture...