I mean, you choose not to interpret it beyond that because to you it's something other people are talking about. To someone who experiences this regularly it can apparently get really annoying, hence the negative reactions.

I'm pretty sure he didn't make a fair point. I haven't taken any thermodynamics classes, but I think the word "spontaneous" means something more specific in this context and is technically accurate.

He's trying to one up her by using the common definition.

So he's wrong on multiple levels here, and there's no reason to pick apart the meaningless social media post accusing him of mansplaining.