A second-half penalty decision was reversed by ref Lee Mason after Florent Hadergjonaj had been fouled inside the Cardiff penalty area.
"I think it is good there was an experienced linesman," said Warnock.
"There was not enough contact for a penalty and the linesman made him change his mind. If that had won them the game I would've been disappointed.
"But I think there was a clear penalty for us on Junior Hoilett in the first half - the lad [Florent Hadergjonaj] did not see him coming and took him out."