The trending page actually shows posts that are massively supported in the community however the truth is I grade this Into two;

First artificial support; this is gotten when your your posts trend courtesy of what is referred to as bid-bots, you pay money to these not services and they increase your vote in kind, putting your post on the trending page, however this is not natural that's why I refer to it as artificial so first the first way will be through bid-bots

The natural support; this is actually when the community generally supports your content because of either the community you're part of or because of the quality of the content which somehow adds value, this way you put your content on the trending page naturally because of it's value or the community you belong to

This is basically the two way