No, it was funded by Google. Advertisers paid money for Google for totally unrelated services. Google invested that money in a number of ways. One of them was

No, it was funded by Google. Advertisers paid money for Google for totally unrelated services. Google invested that money in a number of ways. One of them was to build this very profitable non-advertising business. The advertisers didn't fund that business any more than the advertisers funded US treasuries, or the dozens of startups that Google has invested in as a VC.