It’s coax for cable TV. If you have Cable Internet available in your area, it could be used to connect to the Internet using a DOCSIS modem, but your cable company can advise you. If you have multiple jacks in your home, you can also use MoCA adapters to run Ethernet across your home without having to tear down the walls to install wiring.
He’s right that Windows’ ARM story is still a mess in the absence of anything remotely resembling Rosetta 2. I am looking forward to Qualcomm laptops running Linux, however.
As for dismissing Qualcomm’s performance claims, the big difference is Qualcomm bought Nuvia, which was started by Gerard Williams, the brains behind Apple Silicon, and indeed Apple’s progress since Williams left has been lackluster and mostly due to process improvements, so Gruber is being both churlish and complacent there.