What happened to this stainless steel tool when exposed to vinegar? Based on an article I found online about how to disinfect hygiene tools I've been soaking nail clippers and similar items in a mixture of white vinegar, dish soap, and warm water for a few hours in a plastic sandwich container. 

So far it's been fine, but recently did it with a stainless steel cuticle nipper and after taking it out and rinsing it and drying it off, the metal had turned a dark gray color it's giving off a foul odor. 

What happened to the metal, and is the tool still safe to use?

For reference, here is a photo of the tool (on top) and a different one showing what it used to look like (bottom).
What grade of stainless steel was the clipper made of? Was it labeled stainless steel, or is this an assumption because it looked shiny or similar to some other corrosion-resistant object (which may itself be stainless steel or not)?
Test with a magnet: if they are non-magnetic, the clippers could be stainless steel. Without knowing more about the source of the clippers, I could guarantee you that they are not stainless steel - after, they were not stain-less even in vinegar.
It is difficult to imagine any kind of heat treatment or surface treatment (short of plating with a more active metal) that could result in this kind of generalized corrosion.