Because the referee saw a coming together but didn't see Deeney digging his fingers into Allen's face. He's seen what looked like adopting an aggressive attitude, but I would guess that he has said that having seen the replay he has seen something he didn't see at the time, and had he seen that it would have been a red card. And I can understand that as Michael Oliver was the wrong side to see what the contact on the face was.
Brave, if stupid, move from Joe Allen to go toe to toe with a man who was sent to prison for kicking a man in the head in a street brawl little more than 5 years ago. I'm a big fan of Deeney, especially how he turned his career around after prison, but there is no way he can get away with what he did here.