I'd let them soak in water for a few days to see if that changes the chemistry of the water (outside of any gas off of CO2 from the water) to see if hardness or pH is affected. Sometimes vinegar isn't the most accurate of tests, maybe use a stronger acid if available.
and no pics, because all the rock is in the garage, pending the setup of a new tank, maybe one day.
If the rocks look white-ish, they may be limestone & raise your GH. I would also be cautious if they were from a "landscaped" area, they might have been sprayed with weed killer or other pesticides, not so good...It doesn't mean they can't eventually be used, maybe in a "kid garden" area for a long while.