I don’t know for sure, but it’s probably something as boring and cumbersome as an infinite spawn abuse after bypassing the timer start trigger. If that was the case, they could have gotten any score they like.
That makes sense, and considering the occasional serious bug that can make my eyes go wide for a few moments it shouldn't really surprise me. I mean, I just had the first hard crash I've had in a while so I had a moment to visit the forums. Still tho, it'd be interesting to know how it happened especially if it took everyone by surprise.
Leaderboards are always hinky. I have never seen a leaderboard that wasn't abused by those that think it actually means they're leet. I believe that because leaderboards are not essential in games that the companies cant be bothered chasing down the exploiters. Hell, if they kicked a handful it would be half of the playerbase gone.