What is a speed bump? There is no such thing.
If your Shuckle outspeeded Purugly, Purugly's Speed stat may have been lowered or Shuckle's Speed increased. Shuckle may also have been holding a Quick Claw, or Purugly may have been holding a Lagging Tail. Then again, their Base Speed stats may have caused it; if Shuckle was a higher level it's Speed may have been higher than Purugly's.