It's rare that a citing overturns the decision of the officials on the day. It's not like it was something that just went completely unspotted in real time, it was examined at some length on the day. If the panel issues a ban, they are basically telling the officials that they got it wrong, and so it would have to be an absolute howler of a wrong decision for the panel to undermine them like that. CMK, together with his TMO gave their reasoning for yellow only. Personally, watching in the ground without the benefit of being able to eavesdrop on their discussion, I was fully expecting red, but having heard some of their conversation, they present a reasonable case for yellow only. The officials will be among those putting forward evidence and will be wanting to defend their own decision, so that and, if I'm being mildly cynical, the politics of being seen to back the ref in all but the most clear and obvious wrong calls, will probably work in Gaby's favour.
Not just saying this because we're talking about a Wasps player, but I'm not a fan of too many red cards for relatively innocuous and entirely non-malicious incidents like this one. All for protecting the players and tough sanctions to deter real recklessness, but yellow enough here IMO. Hopefully common sense will prevail.