I know Graham Poll is a plonker, but here's what he has to say:
"He gets suckered in by Zaha's dive, it is a dive, he feels a little touch, he'll claim there's contact but it's not enough for a penalty kick. An experienced ref like Jon should not get suckered into that one."
I haven't seen this particular incident. But since when does contact automatically mean it's a penalty? I know pundits love to justify cheating on the basis of contact, "there was contact there, he has every right to go down" - but contact does not mean it was a foul.