It hasn't worked perfectly though, as the vaste majority of American bisons (all but 4 herds in fact) aren't true bisons but have cattle genes due to hybridation.
There are second hand accounts from indigenous people, excavated bone sites with tools and spear tips, but reportedly no first hand recorded observations from Europeans of buffalo running off cliffs.
Buffaloes aren't exactly Main Battle Tanks you know: it's not that difficult to build fences that are able to stop them (it just won't be the light fences you have in mind).
Also, not voluntarily pushing the beasts to your fences is going to help a bit, since buffaloes don't run to cliff on their own…
I thought that must've been a typo upon first reading. Even 325,000 would be shocking. Amazing that the conservation efforts seem to have worked well.