I am inclined to agree with you, sadly, Artiste after thinking about it. I think OMT was condemning Ennis as a fool.
He was a sad, bitter old man who had lost his farm, his spirit, and, at last, his only son. I think he was consumed with grief and one of the earliest stages of grief is anger, leading on to despair and bitterness.
In fact, now that I think about it, the way OMT acted was similar to the way I saw a few people react after the death of Heath Ledger. It can bring out the worst in people. I've seen people lash out in a vindictive manner, even hatefully. Grief can change people radically. Hopefully it is temporary.
But through it all, I don't think OMT was homophobic because that would mean that he'd be repulsed by his own son. And I don't think that was the case.