I don't have any insider knowledge, but having worked on websites before, I have a guess.
A lot of companies will duplicate their websites with a slightly different URL to have a staging area. This is where they can try out new things on the site, make lots of changes, and not have it affect the actual live site. The error you encountered is likely just a bug due to a redirect URL that mixed up the production site with the test site.
Also, your username and password for this site wouldn't function on that login, as you'd need to be a website admin to access it.
I would say you can just ignore it and if it happens again, try:
-Refreshing the page
-Going back to the homepage, going into your profile again
-Look at the URL in the address field and if you see 'staging-community', just delete the 'staging-' and try again.
Again, this is just a guess, but I was able to go into my profile without an issue just a moment ago, so I'm assuming the bug / error has been resolved.
Yeah - I think it was just a bug while they were rolling out the Admin only group.
You are correct, this was a bug due to some backend Community updates. Thank you for giving us a heads up and for your patience with this! You should be good now but do let me know if this happens again.