My toddler's poo smells like acid?

This morning when I went to get my 16month old son out of his crib, his diaper was full of poo that smelled like acid or vomit or something along those lines - it reeked! As soon as I opened the door, I panicked and looked at his heater to make sure there weren't any batteries or cleaning products or anything near it (not that we keep them in his room, and not that I know what they would smell like near heat, but it was my first thought as to what might be causing the smell).

I tried to do research online, but everything I came up with was really little babies who had milk intolerances or toddlers who couldn't eat certain fruits because of the acid or something... but he hasn't had anything he doesn't normally eat. He's probably had more bananas than usual in the last few days (he loves them and asks for them repeatedly when they're in the house), but those aren't acidic.

I'm just trying to figure out if this is something to be worried about, or if it's just another strange baby poop.