It's definitely worth watching that first video if you know little about volleyball and especially the bit about rotation in conjunction with the tutorials.

So far I've watched the first set of the match of the men's 2021 championship. They don't half hit the ball fast!

And it was a little hard sometimes to work out who'd won some of the points as even when a player messed up there was still lots of high fiveing and back slapping.

When I've played 5-a-side football even if you score a goal you'd look a bit odd celebrating 

That's a great observation Roy.  And it is somewhat strategic.  If you make a poor pass on serve receive, for example, and all players do, the other coach looks to see body language.  The huddle is there after each point (high fiving/back slapping) to get everyone to a "reset" level and forget about the last point and get ready for the next one.

If the other coach sees a player who has bad body language/attitude after making a poor pass off a serve, GUESS WHERE he will tell his player to serve to next?

So the huddle element is to get all players back to "neutral" and ready to go again.  

The alternative is to let a player who has made a bad play go sulk in the corner of the court and stew over a bad play which will then probably impact the next couple of points.  

This is a MASSIVE MOMENTUM type sport where teams can go on long runs with multiple points just by getting the other team negative.