It's from a livestream and then saw at least another additional generation of compression when IGN reuploaded it again. This upload from Epic themselves is ever so slightly sharper and less desaturated (if my eyes are not deceiving me), but it's still only 1080p:

https://youtu.be/hzcsKvrF-Ho

The difference isn't that great, but texture and object detail aren't what this particular demo is about, so it doesn't really matter all that much.