I'm not saying not to use onx or that onx isn't close it's situations, it's when inches or feet may make a difference i wouldn't trust it. Yes a lot of dat is tied in with gps now, but many parcels are not especially if it's never been sold or needed to be done and was sold based on legal description. At that point the plats are plotted off of old descriptions hopefully from a known point but small errors grow the farther you get from the known point.
There is a lot of coordinate adjustments and other factors that go into accurate survey data. Even though surveying is a big portion of my professional career i wouldn't trust myself to go off of city plat and gis data to stake my own property for a fence if there were no property corners found. I'm sure i could get it close with a couple long tape measures and i could put the fence up and 99 times out of a 100 the neighbors wouldn't know any better or make a big stink about it, but the 1 time a neighbor would, i would have to get a professional survey done, if my fence was on their property i would have to move it. Just like in this situation almost everytime there wouldn't be a big confrontation about hunting on or near the property line. but i would assume if the landowner caused a big enough stink and pushed it far enough, had the survey done and were able to prove they were on his property he could charge them for trespass.
This is all hypothetical, maybe he recently had a property survey done on that field for some reason and knew where the property line actually was or had a good idea. Maybe he did decide to stay back a ways with his corn field and the other landowne decided to plant it, or the other landowner planted beans before his corn and this guy instead of planting over his beans stayed to the inside. If we are going to trust a phone gps and onx i don't know why we wouldn't trust the multi thousand dollar gps systems on tractors now days. i could hunt the rest of my life and probably never experience this, but a pissed off landowner can sure create problems like the guy in wyoming about corner crossing.