I was at the hunting lease checking on the deer killed and ran into an old man who hunts there too. We got to talking deer and turkey and he mentioned that he likes to drive around in the spring and just call to the birds to hear them gobble. He apparently just steps out of his truck and his a box call.

He's well into his 70's and I didn't have the heart to tell him that's not a good idea. It hasn't seemed to hurt the turkey hunting there as far as I can tell but how harmful can this be?

The lease is 5500 acres and me and my friend are the only ones to ever kill turkeys there (poachers excluded if there were any). Two seasons open to turkey hunting, three gobblers.
Is there any harm being done by this old man?