As I recall, he did have fence up that would keep "cattle, sheep or other livestock" off his property, but Bison are a completely different story, and the property owners claims and complaints were totally ignored.
Shooting the Bison was wrong, but at least half the blame belongs to the Bison owner.
by law (as I have researched, but if there is a laywer out there, feel free to correct me) if your neighbors livestock wanders onto your property you are entitled to corral it and charge him the cost of maintaining it until he retrieves it. You do not get to hirte a bunch of illegals to begin shooting it on your property and then chase it onto a thrid party’s and federal property killing as you chase, then leave the carcasses to rot.
BTW, Park county had record snowfall this winter with 25 foot snowdrifts. All kinds of critters were walking over the tops of all kinds of legal fences