Winter is here so maybe Daenerys wanted to warm up with a hot cup of Starbucks coffee.
It was quite obvious that a Starbucks cup was left on a table during a pivotal scene in Sunday's show. If you want to check it out on TV, look for it at about 17:30 in.
HBO has responded to its slip-up. In a statement, the network said, “The latte that appeared in the episode was a mistake. Daenerys had ordered an herbal tea.”