The deal is between sky and C4 and on the surface does not appear to involve Liberty. It only mentions 2019 while sky have the exclusive rights to F1 through to 2024 in the UK.
I have not seen viewer figures in recent times but C4's were much higher the last ones I saw and I would imagine that FOM would like to see lots of eyes seeing F1.
https://www.channel4.com/info/press/...o-more-viewers