I believe that it might be a system error. This sort of thing happens from time to time. But if you're not comfortable with it, you should contact your email administrator to get any clarification on it.
I don't know what email system you are using but there must have been some sort of glitch when you tried to log in and it failed but it wasn't anything major if you managed to log in again without issue. Sometimes email systems can be a bit buggy so I would contact your system administrator and see if they know what happened so you can be aware of it in future perhaps?
