That old Spanish silver circulated longer than many of us imagine. Even after it no longer legal tender in 1857. It's great seeing that old stuff show up in the context of CW sites - even if it can't be definitively proven as a CW drop.
Pretty confident that this was dropped by a soldier, it's a pure camp. Only one other coin has been found in this late War site and that was an 1864 Indian Head penny. It was a real surprise to see this pop out of the ground, made the day for me.
I've found a couple pieces of Spanish silver in a pure CW camp, but they were extremely worn due to being in circulation for so long. I've also found more early silver at camps that were adjacent to an 18th century homesite, but it sounds like that's not the situation in your case. Nice find regardless.
When it first came out I was hoping that it was a seated, and couldn't figure out why it was so worn. Being 89 years old in 1864 explains the wear though. [emoji16]