Can't be sure. I just assume that what is trending in cmc is the most typed word in the search field during a certain period. However, the marketers I found on twitter use the reward method to perform certain tasks including adding their coin profile to the watchlist and some social media account boosts. And another fact, cmc also collects visitor cookies.

I doubt that the cmc team will explain the algorithm to be trending, because after all it has to be purely generated.