I strongly suspect Comcast aren't going to build an access network in the UK, or anywhere else in Europe, from scratch. Sky have a pretty fantastic deal on Astra transponders that makes it difficult to justify spending billions replacing them with a terrestrial transmission network.
Comcast's technology is nothing special it's just standard DOCSIS 3.1 alongside some metro-Ethernet.
I suspect they are after the content more than anything else, much as 21CF are. That said given they mention an interest in European assets and obviously that alongside the massive content business they are also the largest non-international cable company in the world they might start looking at Liberty Global as an option. In between dodging significant non-essential capital expenditure on cable networks outside of expansion Liberty have had the odd foray into content.