Well, if it wasn't bubblestrat, then maybe it was some other half-decent way of leveling a gym, like magikarping. Looking at Ledyba's strong defense, I can only imagine that they might have been Shucklin' that gym. His double-SE STAB Rock Throw could take out a Ledyba without needing much healing. If Ledyba has Tackle, he's even resistant to her quick attacks.
Like you say, it might also have been 17 eskimos crammed together in that car, banging down the Ledyba for 100 prestige each.