Wouldn't worry too much I don't think they've had a
Trip advisor style breach I've also got a unique email address for BA and everyone else. The funny thing is I have a friend who shares my paranoia and we each have an address that we only use for contacting each other. Somehow I've received spam sent from her address recently and we have both checked the mailboxes and never sent anything from those addresses to anyone else. Chances are, as in your case it was just a
(n un)lucky hit.