Gray's side were winning 1-0 at the time but eventually slipped to a 2-1 defeat.
He said: "I've got no problems with the second booking. But Paul's first booking was his first challenge in the game and it was done with no malice in it.
"The referee just seemed to dominate the game again. He was consistent - he gave us fouls and he gave them fouls.
"But the sending off was very harsh and I just felt that at times, he didn't let the game flow. The referee shouldn't take the centre stage."