so let me get this straight, you transferred a quantity of gold from your account to another account that isn't on the same bnet?
If you did, that's what got you banned (in my opinion), it seems to me that blizz tracks large transfers of gold between accounts, and assumes that you are selling that gold for real world currency.
To put it in context, the only ban I've ever had, was when I shifted guilds, deposited a bunch of gold in their GBank (about 15k) and then a couple of days later, left that guild. That must have triggered something in their system, cause about 20 mins after I left the guild, the banhammer hit me.