Can someone please explain to me what this is all about?

The way I've understood it is Shannon showed that it's possible to reliably send a signal even if you know the signal will get corrupted before arriving at the other end.

Shannon's theory is foundational to modern communication systems. You can expect to have WiFi remain functional even as other devices use the same medium. Up to a point, the Shannon limit in other words.

I've added an explanation to the toptext which is taken from a comment by DonHopkins, who recorded (but did not submit) the video: https://news.ycombinator.com/item?id=49622607.

Hopefully Don won't mind!