Documentation of Questions is not really that good and hard to navigate. The part of statistics can be found here: https://confluence.atlassian.com/questions/administer-questions-593035916.html
But as you may have seen it says very little. So guessing a bit with the extra info of your 8000 users and if it is as you say that it is not the space users my guess would be that you have a macro displaying questions in the dashboard and the software records each individual users that see that macro as an active users that look at questions.
Posting the answer found if incase anyone else is looking for this. Its actualy the users who involved in creating the questions/answers/comments, found this by the filter option provided by the statistics itself. We had some spaces with few questions, while viewing the stats for that noticed this.
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