krissy that's because even if that video is captured in "1080p", they haven't super-sampled the video to take into account the deinterlacing interference. That's practically a 1080i feed deinterlaced and encoded as 1080p, causing it to seem like it is in half horizontal resolution. They should have had the game rendered in 2160i and had that deinterlaced and encoded as 1080p.
In fact, they could have pushed it even higher to give a full supersampling effect in place of antialiasing.