This doesn't sound like he was hard of hearing.
Do you think he actually heard the part about him making drugs with this stuff? Until, now, I would have wondered what the hell the guy was talking about making drugs. That is, if I had heard him say it. I'm hard of hearing my self. Lotsa times I just agree or whatever, when I don't full hear what someone has said. I get tired of, I know they do too, of saying, "HUH", all the time.
The old guy probably didn't know what he was even talking about.