He was booked. But as of July 2013, if the referee wasn't in a position to fully assess a challenge, players could still face retrospective action, but that is a power the FA will only use sparingly.
Look at this website. We don't all agree. It's not about all or nothing. There would be both, some fans admitting it was a dive (as I assume some palace fans will, maybe not those that come on here, but the reasonable ones) being embarrassed, asking how we can dare criticise Zaha after Knockaert...
I point you to Niasse for Everton against Palace - ref saw it, gave a penalty. Niasse was retrospectively banned for diving, despite clear contact. For years, the gold standard has been 'if there's any contact it can't be a dive' so I was surprised they banned Niasse, but they have set that...