That's not a DDOS – it's called “actually delivering the service your customers paid for”. If you've underprovisioned your network, that might be a problem but it's not an attack.

It's also something of a best-case scenario because the only party affected is the same party which has the ability to fix the problem: since it's on your network, you can add additional capacity or institute some sort of fair-queuing without the need to negotiate with outside companies.

I imagine the Open Connect box would do automatic bitrate tuning for all users on that network for immediate mitigation and notify obviously Netflix and the open connect ISP for long term capacity management.