I don't know much about codecs but if 2h of 4k footage are 50GB, it must be compressed somehow.

4k normally means the same as UHD which stands for 3840 × 2160 pixel. As far as I know 4k actually is a different standard with a resolution of 4,096 x 2,160 but I would assume Sky to stream with an aspect ratio of 16:9 so they probably mean 3840 × 2160.

UHD resolution results in 8,294,400 pixels. I don't know much about color depth and it seems to more complicated than I thought because I thought 8-Bit Color Depth refers to 8 Bit for Red Green and Blue but 8-Bit color seems to be something different (much less color information). Anyways... 8 Bit of information for Red, Green and Blue is pretty basic if you wan't true color I think.

With 8,294,400 pixels and 24bit (3 Byte) per pixel we get almost 25MB per frame.

I don't know the framerate sky will use but the lowest TV standard is 24p meaning 24 full frames per second. That would mean a second of video would require 600MB and a 2h F1 Race would be 4.32TB.