How does blog views count work?

Previously, I had the impression that blog count increments after each page refresh.
Today I tried to check if this is still valid.
I opened a blog: HANA Rules Framework (HRF) blog of blogs in anonymous mode (not logged in) in a separate browser (Pale Moon Portable 27.0.3) and started refreshing the page:
This is the initial state (527 views):

Then I refreshed the page and saw this (486 views):

Are there several sources, which determine the view count and are these out of sync?
I can completely understand blog view count incrementing, but decrements probably indicate a problem somewhere...