I was signing in to the PS forums on a computer that only I use. It auto signed me on, but as a totally different user. So far, this has happened only once, but it was very odd.
Maybe we shall all end up wondering whether we are we or someone else in these forums.
Your issue may be related to another one most recently reported here:
Yep that looks like the same thing going on, Jacob.
Do you recall the name of the user you found yourself signed in as? And about what time it happened (including your time zone)?
I will also follow up with you via email for more details.