Sounds as if it weren't aged properly, as that is the process that tenderizes the meat. Or, an old cow can be tough even with normal aging.I don't know how long you would need to grain feed a cow to change the meat but I do know a couple of weeks will only change the cow pile. Me and my wife bought one from a man several years ago to butcher and he said he had corn fed it for a couple of weeks. Well that thing was so tough you couldn't chew it. We were teenage newly weds and learned a lesson for life. Looking back 50 years ago I guess I have saved a lot of money on beef from that experience. As far as the ferel cow goes, it belongs to someone.
I grew up with cows all my life every once in a while they decide they want to roam and a 10’ tall brick wall will not keep them in. In 7 years of living in the neighborhood this is the first time he has stopped by looking for them.Your neighbor should've trained them better or learn to build a fence