People say that to mean the actual action of kicking something, not the motion of bucking. Is that grammatically correct?

People use it either/or, leaving it to context.
With Rodeo Bronc-busting and Bull Riding, its usually the second meaning you said and as little as possible of the first.

From what I have heard and consider the word "fuck" is derived from the German word "Frichen" which means "To strike" so if the word "buck" is taken into the same consideration then I can assume from the current usage of "fuck" then it could be considered the same for that purpose.

Oh this might be better for the explanation:

1774882 that was fucking inform-a-fucking-tive