I Sit On Acid first came out in 1988. But the drums do not sound the same as HBHG. Furthermore, I'm not sure how anyone can be serious about drum programming plagiarism really. Unless it's something really distinctive like Plastikman's
Spastik or Moby's
Thousand which are basically just drum tracks. Even things like the Winstons' Amen Break or James Brown's/Clyde Stubblefield's Funky Drummer didn't get them any royalties for those samples of their human performances...
When I first read about it I wondered if there was more to it, and indeed I asked a similar question to yours on the previous incarnation of this forum
HERE. As you can see, no one here really understood Praga Khan's position when we discussed it in 2014.
ps: I Sit On Acid 2000 actually came out in 2001.
DON'T. LOOK. DOWN.