TBR Bio II.13 Chelation

I am having trouble understanding this question. The passage suggests that a good chelator allows anchoring of gamma carboxyglutamate along with Ca2+ to bind with coagulation factors, thereby aiding in the formation of a clot.

Q.13 asks what bests prevents clotting, and the answer explanation said that a good chelator has most carboxy groups.

These two statements seem contradictory. I looked up chelation online, it seems to be a good anti-clotting agent. So how do we explain it's effect during clot formation at sites of injury?

Thanks.