The Statistics tab and information is retrieved from a module of the add-on. To disable this tab to appear, you can go to Confluence Admin (cog icon) > Manage Add-ons and search for the Questions add-on, through the User Installed Add-ons tab.
There, click on the Confluence Questions tab and search for the 227 of 227 Modules Enabled link. Once you click there, it will expand all the modules of the add-on. Then, you need to search for the View Statistics module and Disable it with the button in its right side.
Once you refresh the Questions page in your confluence, it will not display the statistics tab anymore. However, you can still access it with its URL, which would be - http://baseURL/questions/stats.
PS: Remember that the Usage Statistics content is only displayed to users with properly permissions, as we can see in our Questions article.
Hope it helps you!