probably down to the way it was programmed
it was all done on the 909 ( as a master sync) and recorded live ( is my guess) and it's very easy to nudge that tempo knob.....

also all the editing back then was done with a razor blade and tape so none of this " snap to bar" type editing that we do today at home.

it's an oldie for sure

god know how many times it's been remixed , in fact i think there was a new one around not so long ago?