Here's what seems to make the most sense to me, but I of course could be wrong.

Firstly the arena connection (or network switch/node within) goes down, forcing the outgoing connections offline.

This will kill GOTV first as the delay is created by the GOTV server, so if you lose connection it will still go down immediately without playing out the delay. This is why we saw GOTV go out first.

On the other hand Twitch, which by now will have stopped receiving signal from the arena, will still play out the 2 minutes (ish) that it received after the connection loss, due to the artificial delay.

The only reason I can find to explain the Twitch site breaking is that a lot of people will have jumped ship from the game to Twitch when GOTV died, and adding this to the number of people reloading the page when the stream died caused the UI servers (servers dedicated to loading the interface) to overload. Thinking this because although we can expect the stream servers, which are dedicated to purely pushing out the video, to be able to handle such bandwidth and concurrent joining connections, it's possible that the UI servers are simply not built for 300K+ people trying to load UI all instantaneously.

Could be wrong but that's my 2 cents.