I don't think NPCs can compel a PC's Aspects, only the GM can.
A PC, however, can compel an NPC's Aspects, I think, and in those cases the NPC gets the Fate Point.
One of the best moments of our game was early on, when I compelled the wizard to try and keep the rookie Knight of the Cross out of things, and also compelled the Knight to insist on being involved. It forced our first Social Conflict, which was hugely entertaining, and helped us all get a firmer grasp of the mechanics.