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 dont know if there is 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.

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