The Views counter is not updated the exact second the topic is viewed. Each "view" is logged, then at a set period of time, a CRON runs that updates the Views counter for each topic that has been viewed since the last update. The counter is updated this way to cut down on the massive number of queries that would run to update each and every view as they happen.
XenForo doesn't keep track of unique views by default. Every successful render of a topic counts as a view, so if you refresh the same page 10 times, 10 views would be recorded for that topic. But the counter won't update the same moment.