But I doubt it was the transit pipes because Google doesn't use those for free, as far as I know, nor does anybody else. Some large ISPs have no-accounting peering but they pay for their own transit to the peering points. Google, it is reported, buys a lot of long haul pipes, more than many ISPs.

Free peering has always been a controversial issue. Large ISPs peer with one another for free, smaller ISPs pay to do this, though in theory only paying for transit. But what makes an ISP an ISP? Can't Google or YouTube argue they are an ISP (with very popular data) with one giant customer, bigger than the combined customers of many medium sized ISPs.

Who is the traffic for? When I search Google, it's for me. When they present me ads, it's for them. The internet decided on the "I pay for my half, you pay for yours" rather than trying to figure out who the traffic was for, and having "toll paid" traffic and "800 number target paid" traffic like the phone system or the X.25 networks. Who won?