This disclosure says that everyone who was hacked had their email inbox hacked. So you're saying that someone hacked Coinbase to find your email address, then once they found your address, hacked your email inbox some other way, then used that to hack Coinbase? That sounds very roundabout, although I guess not impossible. I guess it's possible Coinbase could have some info leak somewhere that would leak your email address.

Did you ever use any other cryptocurrency website? If so, one of those could have been hacked in order for the hackers to get a list of users to target.