That actually sounds exactly like something he would do. Shake your hand with a sly self-righteous smile and then spit in your face when it came time to deliver on the agreed terms.
Delivering 2 proposals would be going above and beyond and giving the community 2 extra HF choices instead of one. This would be fulfilling his end of the agreement and going above and beyond. Having many implementations is a good thing right? More choices and all.
Sure it is all fine and dandy to make various idle threats to withdraw poole mining power - but it is a very risky move to actually attempt some kind of politically divisive action, and then potentially lose mining power when miners move to other pools because they don't want to support such unnecessary and wreckless attempts at blackmailing (that even under decent scenarios seems likely to fail)
Antpool does indeed seem to be reinterpreting the agreement (to assume that those devs magically spoke for core as a whole and could make decisions for the community) with the assumption that was very carefully and clearly refuted before they signed the agreement.
I don't think their threats to withhold segwit will last long and hold as much weight as the threat to switch PoW algo's or dump BTC for alts*
* All these threats are credible but unlikely. In business, smart negotiators give credible threats, and are willing to walk away from the table, but it is unlikely to happen and compromises will be made and the long negotiation will continue.