Not sure if it was acid, but leaving nickels in a vinegar bath for too long will definitely cause this type of outcome, etched.
It's definitely been exposed to something corrosive. Acid seems like the most likely possibility. Vinegar is acidic enough to do this if the exposure is long enough. It could have even been buried in some acidic soil.
In my experience an acid or vinegar bath would have brought some more detail out of the reverse. So it would probably not done on purpose. Acidic soil might be the culprit.
Looks like it spent some time in the ground. Or some type of wet enviroment. As a kid i would "wash" 1 cent pieces in vinagar with salt mixed in, it would really eat at the copper.
It looks more like environmental damage, to me. This coin looks like it was probably buried for decades, and then someone found it metal detecting, or something like that.
Definitely looks like it has been in the ground with an attempt to clean (tumbler?). I've found lots of them over the years, a small number seem to do ok but most look like the OP's example. One of my favorite designs and always leaves me a little melancholy when I find them environmentally damaged.
