Needed: Plausible explanation for Facebook password reverting back to an old password?

Here's the situation: I was suspicious of my boyfriend's behavior so I tried to get into his Facebook account. I knew the password for his email and I also knew his previous Facebook password before he changed it. So I got into his email and had his password reset to his previous Facebook password. I want to come up with a plausible explanation for why that would happen without him getting suspicious of me. I didn't really change anything in his profile so really the only thing he would likely notice is that the password is not the one he was currently using. I want him to be able to resume use of his Facebook account without him thinking that someone hacked him because then he'll be suspicious. What is a plausible explanation I can use if he asks? I was thinking of maybe telling him it was a temporary glitch that got fixed so hopefully he'll buy that and drop the subject but I want other ideas just in case.