I think the ability is poorly worded by including the phrase "choose to." In the sense that it says to choose to: heal all damage AND end your activation. It implies that you have to be able to choose to end your activation, which you can't do because the Pig isn't activated. If you can't choose to end your activation, then you can't also choose to end your activation AND do something else. See previous discussion on the issue here:
However, I believe the intention is more something like this: "Eat Your Fill: After killing or sacrificing an enemy model, this model may choose to heal all damage. If you do so, end your activation." This would make it more clear that the activation ending thing is simply a consequence of using the ability, which I feel is the intention and proper interpretation of the ability.