Was it REALLY a Samsung Galaxy II And a genuine Samsung Battery, or was it a Knock-off? If it was a Fake, the Battery safety protocols may have been circumvented, and that's why it blew out. If you don't screen the batteries. or sort them out, and they are factory rejects, the chances of this happening are much greater. Also which battery blew out? If the replacement was a secondary market spare, and he shorted it out with something in his pocket, well, that's not the smartest safety protocol, either. Most batteries have a safety circuit, that shuts down shorts & keeps these events from happening, Unless the battery itself is faulty.

So is our other proud sponsor, Airbus.

Couldn't resist.

An upcoming software update will address this issue.

That is likely the problem right there. Unless he covered it somehow the spare battery's contacts were exposed, which makes it REALLY easy to short across the contacts, especially in your pocket. Some change, a paper clip, keys, or really anything metal in there and you have a recipe for an exploding battery.

Does this mean I shouldn't be carrying around a spare laptop battery in my Captain Kangaroo blue genes?
Or put another way, probably good that lithium batterys weren't around when I was a kid.

I would expect an explosion to do more than second degree burns...

I guess it gets more clicks though

It's a matter of how quickly they can discharge. How much current they can deliver for a short period of time.
See previous post.
It's a good thing they weren't around when I was a kid.