Remeber that youtube has to do an incredible amount of caching and load balancing to be able to handle their workload. Many things can go wrong, especially for short periods before their sanity checks detect failures.

I would more suspect something broken in Youtube's network. Youtube's load balancing system could have been trying to retrieve the video from a broken server that had not yet been removed from the pool. Try to access that video from another IP Address, and the load balancer sends the request somewhere else.

I have seen similar failures in my comparatively tiny datacenter, especially when one server is misbehaving and the load balancer thinks all the servers are sane.