. . .
That's the thing. You recalled your account right? So of course, the buyer is complaining to blizzard, maybe he also said that he has bought the account from you.
What blizzard does?
They check up the IP logs, and since you didn't perma banned your retrieved account, they have checked up also where characters has been transfered. And they saw on which account your mage was transfered, thus easy for them to ban that account.
All in all a loophole:
Blizzard did a investigation on your retrieved account, they saw that there was a transfer that occured between your newly made account and retrieved account, I don't know for what reasons blizzard bans you but at least they got a link between those accounts and can punish you in any way.