Is there a reason for returning only the first card of the dealer in openAI Blackjack-v0 in function _get_obs or is that a bug?

Question

https://github.com/openai/gym/blob/master/gym/envs/toy_text/blackjack.py

In line 113:
return (sum_hand(self.player), self.dealer[0], usable_ace(self.player))