The Geneva Convention says nothing in particular about hollowpoints, so the verbiage has an "interpretation" by DoD about the Rules of Land Warfare that skirts around the issue . See https://www.justsecurity.org/25200/dod-law-war-manual-return...
I know this because I carried hollowpoints while deployed in an anti-terrorism capacity.
It explicitly prohibits frangible/flattening/expanding ammo in war. The US hasn't signed that, but in practice they adhere to that part of it (but yes exactly as you point out, only for "war" not "anti-terrorism")