I have a longstanding hypothesis that Mallus are not actually South Indians, but Bongs who have migrated to South India.
Consider the similarities. Both communities make delicious fish. Both have a tendency to elect communists with mind numbing regularity. Both are soccer fanatics.
Still not convinced? Both of them speak languages which are completely unintelligible to other people. They both make and appreciate art films that nobody else understands. And both refuse to work while in their home states, but turn into exemplars of hard work and productivity when they migrate.
I’m not saying it has to be true, but some testing for genetic markers could help settle the question.