In order to show you personalized data on the site we need to match your HSReplay.net account with the Hearthstone account you play with. Occasionally this this may lead to you seeing a battletag you do not recognize or might recognize from your friends list in the account dropdown in the top right on HSReplay.net.
To remove a Hearthstone account, visit the Connected Accounts settings and click "Remove" next to the account you don't recognize.
If you have accidentally removed a Hearthstone account you still use, simply upload a replay with a deck tracker for it to appear again.