Except they don't "literally" explode. They catch on fire and melt, if you think that fits the definition of explode I have some fireworks that I would like to sell to you.
Explosion: A release of mechanical, chemical, or nuclear energy in a sudden and often violent manner with the generation of high temperature and usually with the release of gases.
This is definitely a description of what happens to the batteries.
I think he's trying to argue that because they deflagrate instead of detonating, it's incorrect to call the process an explosion. That's the only thing I can see that makes sense, at least, incorrect and apparently disingenuous though it is in this context.
This is definitely a description of what happens to the batteries.