That is the clue, all they can do is a database lookup and hope and pray that is is accurate enough for the intended use-case. Really geoIP is snake-oil and not terribly good at what the sales-men claim... (again with the caveat that is does a sufficiently thorough job for content distributors to show good faith to the content licensors that they stick to the contractually agreed distribution boundaries; but for user-tracking for an advertiser (this thread's threat-model?) it certainly is unusable (unless your ISP gets in on the 'fun' and fills the location database in real-time).
I was quite aware of that, I just thought it was amusing. I'm not one of the tinfoil hat brigade, trust me 
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It doesn't show a lot since I didn't enable javascript. Though there weren't many using the latest Firefox on Ubuntu, only 0.72% last 30 days it seems. (But Firefox 79.0 is only 17 days old.)
amiunique.org shows that when you connect to a VPN for anonymity, and Javascript is enabled, you can be tracked easily. You don't need any IPv4 or IPv6. Welcome in the new world.