Thanks a lot for the question!

In short Steeve is trying to filter out votes which are too correlated with the paid bids by the author. Those votes contain bidbots, vote sellers (using vote markets) or just voters who vote predominantly on prepaid posts. We find that those votes don't correlate with the quality of the post, so we're trying to arrange our trending pages without them.

For future reference you can also find the explanation if you click on the percentage. :)