OK so foremost, I don’t think there is any specific meaning to the word “kuttush” in Bengali. It’s gibberish. It’s just a cutesy word that you say to a cute animal. I don’t think it came from Malayalam either. It’s a completely separate language. The Malayalam translation for Tintins dog might be a different word too.

There could be a meaning behind this word, but I highly doubt it’s anything beyond just sounding cute.