You were one or two steps away from a full on sympathetic meltdown, the only thing that might have saved you is you had it pulled out so some of the heat could dissipate. Those cells are most likely swollen with Hydrogen Gas from the chemical reaction, along with god only knows what else.
what usually happens is one or two go, they ignite, and the hot gas acts like a blow torch cutting it's way thru whatever else in it's path, normally the other battery cells, and in the process, creating short circuits all over that battery plate, which they all are connected to, so the rest have somewhere to dump their current into, and swell, and eventually burst on their own, OR get dragged in by the fireball that is engulfing the case. The heat of the fire and the heat generated by them being short circuiting and their chemistry going to 10000 percent just dumping every amp they could ever possibly make, into the fire and melted bus is what makes them so bad, and difficult to put out.
Yes driving with that is extremely dangerous, they still had plenty of power left in them, to be shorted, and pop and fire all over again. All it would have taken is for you to hit something and any bit of whatever touch opposing bus'.
I recycle these, and yes I get many in similar condition from the RC community. My first step is to generally drain the power. If I can safely do it, I have a whiz gizmo I can suck them dry safely and put the power into my electric grid. Then disassemble and get what i want from them.
If I can not do them safely, Ill just puncture the cells to guarantee they are compromised and shorted, throw them into a bucket of slightly salted water and let them burn out. (I used to just shoot them, again, fun, entertaining, but the smoke is nasty and didn't want to let the neighbors have to put up with it, so water it was to keep that 'mess' contained.)
It's rather fun watching them progress, the cells will bloat,. fffffftttt, POP Poof.. SSSSSSSsssss then the next one, the same thing down the line until they all have ignited and burned off. Yes there are better ways to neutralize them, but I was going for cheap. anyways
Please be careful with this and also remember, it might be at or near it's original voltage of what 100 volts or so? that by itself can easily start a fire or kill you if you come across it wrong.
Be careful
Aarom