Child constantly touching cat's nose, what can I do?

My son is almost 9. I know he has mental problems (ADHD/ODD) as diagnosed by an MD. He is extremely obstinate and hyperactive but is good academically. Anyways, a strange behavior started since he started playing Minecraft and I don't know if there's a correlation. He will rub/touch cats noses and say he is "mewing them". We have asked him to stop and even mentioned it to his psychiatrist, who just laughed and ignored it. We think its creepy and wrong. Why might he do this and how can we make him stop?

Added (1). He says mewing means rubbing their noses.

Having experienced Minecraft I don't think there's any connection there. If he was hitting it with Fish then yes, I'd be worried and it probably is Minecraft.
You should try asking him what he means by "mewing the cat" and why he does it.

Its properly just a little thing that the kids are doing nowadays. I wouldn't worry about it.