Two toons from account online simultaneously?

I have one wow account with 2 80s on it, this toon and a warlock. Last night I was playing my warlock and this toon signed on =O I sent a whisper and he logged off immediately. I opened a gm ticket right away saying that I thought I might be hacked and ran some virus & malwarebytes scans but nothing came up. I was able to keep playing for a few more hours last night.

This morning I tried to login and it said my password was invalid. I thought I was done for but I was actually able to request a password reset and log back in (did all of this on a different computer than my main one just in case it was compromised). Once I was in I saw that my ticket had been responded to and that they were doing an investigation into my account to see if anything fishy was going on. Could this be why my password was changed/locked out? I didn't notice any items missing from any of my toons or from my guild bank.

For what it's worth I do have an authenticator and in addition to doing the virus scan I did a search for the "emcor.dll" file that's supposed to be related to the recent man-in-the middle attacks and didn't find anything.

My main questions are:

1. How is it possible for two characters from my one account to be online simultaneously? I had a GM ticket open on this guy about not getting credit for an achievement which was also resolved last night, would a GM have been able to or needed to login on the account to fix something like that?

2. Is it standard policy for an account password to be changed/locked during an investigation? Wouldn't an email or something be sent in that case?

I'm hoping that I'm just being paranoid but I'd love some confirmation. Thanks for reading!