If I had to guess, and it really is just a guess..

When I use tapatalk, I can see that number, and the one that looks like a sheet of paper.
My guess is they keep track of the posts made from computers and phones, and thats the one that is next to the paper (currently almost 360k).

The one next to the tapatalk icon is counting posts made through the app!

..I think.

Pretty neat!