>Google is probably the only non-telco who owns significant infrastructure. So other than Google, the only other option for YouTube would have been a telco
They both have a lot of datacenters and private fiber between them but neither has anything like the ISP peering network that Google owns. Not even close.
They don't own. They's recently (in the past 5 years) started taking part in building, but they don't own anything compared to Google and the major telcos.