Why did car just overheat and aftermath?

What happened exactly? Was it that keeping it on 4000 rpm for 5 minutes caused overheating and this had nothing to do with the connected battery, or did battery have something to do with it?

You were holding the engine at (relatively) high RPM for a sustained period of time with essentially no air flow over the radiator. That being the case it was going to struggle to get rid of the generated heat and therefore it overheated. The connected battery likely had nothing to do with it.

I also saw steam coming up from where the coolant was dropping(onto wires). Would this mean the wires were burning? I didn’t want to go to close at the time.

It's not clear exactly what the wires are you refer to - but the steam could be a result of the high temperature coolant no longer being under pressure and therefore boiling away, it's possible the wires were also hot, particularly if the wires were the ones running to the other battery and thus carrying substantial current.

On the bright side battery went from 2.5 volts to 11.66 volts In the 8 minutes. Does that mean it has been recharging or is capable of being recharged or is it still dead as was before?

Sounds like it was charging - but this is a poor way to charge near dead batteries. You aren't replicating the proper charging curve of a decent charger.

I was trying to charge quicker by revving higher.

This will have helped provide more charge (alternators don't often kick out much in the way of charging current at idle) but it's not a great way to charge and puts the charging car at substantial risk of damage. Buy a proper charger, it's a lot cheaper in the long run.

the latter few minutes in which I could smell something burning

Here's a free tip - if you smell burning don't ignore it!