"Breached" implies that sensitive data, like payment details, private communication, or physical addresses, were leaked. Instead, this is just semi-public stuff like email/username/name. Maybe a better title would be "15M Trello users have been identified (name/email)"
Of course. But are you sure “identified” is correct word here? I chose “breached” because title of mail was “You're one of 15,111,945 people pwned in the Trello data breach”
I think it's reasonable that you chose that title based on the email header, and I also think it's very irresponsible of haveibeenpwned to send out an email with that subject line. They absolutely should know better.