Are you speaking of that black "gauge" directly above your photos, on the right? The "Members Social Activity Meter"? If that's what you are referring to, it is explained that this rating is based on "This is based on members comments, votes, "likes" and private messaging."

You mentioned, "A lot of traffic on my page ranking very low in the trending category, then have very few people visiting my page and rank high". If you are speaking of the black gauge number, that number has nothing to do with how many people visit your page, vote and/or comment on your pics, or send you messages. It has to do with you visiting other member's pages, comment on and/or voting on their pictures, or messaging them (responding to their messages counts).

And as for the "metric used in the algorithm to determine this?", my guess is that is admin's well kept secret.
--------------------------------------- added after 21 hours

By the way, you're welcome.