"mallu" is a popular short form of either 'malayali' that means related to the malayalam language that is the native language of kerala state, or can mean anything native to kerala.
kerala historically has a big presence of the socialist/communist movement because of which kerala is the indian state with the highest literacy rate.
but yes, in recent years the mullahs and the saffronis have made prominent presence there... there are a lot of kerala people who for decades have gone to the gulfi countries and this brought in wahabi thinking that in turn allowed local tableegh jamaati thinking to be amplified... two tableeghi groups that have misled the muslims there pfi ( popular front of india ) and sdpi ( social democratic party of india )... these two groups have spread to tamil nadu and karnataka states.
also, it was in kerala that some of the catholic churches first created the false scare called "love jihad".