What do civicrm extension "current usage" statistics indicate?
What a site sends back to civicrm.org is just this: https://github.com/civicrm/civicrm-core/blob/506fffd478a7d322fbea786c35787c95a6dbe290/CRM/Utils/VersionCheck.php#L238-L240
name, enabled, version
One thing to note at https://github.com/civicrm/civicrm-core/blob/506fffd478a7d322fbea786c35787c95a6dbe290/CRM/Utils/VersionCheck.php#L139 is that it's only sent back for beta and stable installs. Alpha dev sites do not send those stats back, but release candidate testing sites do.
Also note that it does this when its cache expires (3 days, or when cleared). It also up to a point depends on site cron.
Whether civicrm.org further scours the internet for more data to match it up to your birthdate, friends, and latest purchases I don't know - if you can find where the code for stable.php is at https://latest.civicrm.org/stable.php it will say what it does with it. It probably just stores it.
When it's displayed on an extension node, I believe it comes from the update() function at https://lab.civicrm.org/marketing/civicrm-website/-/blob/1f421835b1bc0ad2ce45a919215a6794955aa208/civiext/org.civicrm.civicrmorgstats/CRM/Civicrmorgstats/Utils/Extensions.php#L31-41, which in turn gets it from https://stats.civicrm.org/json/ext/{extension name}.
I believe that is somewhere at https://lab.civicrm.org/infra/stats-collection, but I would think just pulls it from whereever stable.php stored it.
So without seeing what is actually installed on civicrm.org, or knowing how often that update() function runs, half of this is guessing, but it's clear what a site sends back.