This is the exact wording from your states hunting regulations, so if he has permision from the land owners he is alright, or 100 yards from a domicile, not just the property line.

It is illegal to:

Shoot a firearm within 100 yards of a building devoted to human occupancy while on lands you do not own (including public lands) without the permission of the owner or occupant of that building.

I know your frustrated, but I would not go accusing people of things that are not illegal or that they haven't done unless you know the law and prove they did it. It will backfire every time I promise.

I would suggest talking with the guy and telling why you hunt when you do. Tell him your truly sorry if it bothers him, but it's the only time you can find time to hunt. Let him know your not lazy, you just have other priorities and commitments that have to come first. If he doesn't like it I guess he should work on purchasing his own land so he can hunt it the way he wants to.

My take on it anyway.

Paul