The Latics boss is still waiting for his first win since returning to Boundary Park and he was left disappointed again after Williamson awarded Orient a contentious penalty before turning down an appeal from his side.
"I hate criticising referees," he said. "They have a very hard job, but I don't know what he was thinking when he gave the first penalty (from which Orient equalised) and when he didn't give a second penalty (following claims by Oldham).
"I can only assume he was too close to it.
"They have equalised from one penalty with their first shot on target in the game and with the second one our lad (Chris Taylor) had no need to go down. He was clear in the box.
"I hate criticising referees. I try to be supportive but his performance has unfortunately influenced the result instead of complementing the game, which is a shame."