It's based on Google account. There might be other vectors too. I tried browsing lots of pages in incognito, making Google searches, clicking ads etc. but that

It's based on Google account. There might be other vectors too. I tried browsing lots of pages in incognito, making Google searches, clicking ads etc. but that didn't help (might work in long term). Signing into my Google account (with history) was enough to pass the test.