The way he's using that boot is a bit more sophisticated than Al thinks. It acts as a kind of metronome, but he doesn't follow it exactly; quite often the downbeat anticipates the stamp at the start of a phrase and the tune catches up in a couple of bars.

All three tracks have subtly flexible timing. He can only do that because he's playing solo - anybody else in the mix, however good they were, could only make it more rigid and rhythmically less interesting.