Could be that someone at Lastpass simply does not know how to write properly.
Maybe the attacker attempted to use the master password login festure without having the actual correct master password itself, and the email is poorly written.
Unfortunately, I just tried and that email is sent when the correct master password is sent.
When someone uses the wrong password, it doesn't send any email. (That event is logged though, and I see those failed attempts in the dashboard -- those, I'm less worried about, obviously)
Maybe the attacker attempted to use the master password login festure without having the actual correct master password itself, and the email is poorly written.