This is a nonsensical argument to make .You claim the study to be stupid on what basis, you said they only chose select groups of people that are tall and claim them to be too small to make a difference .Yet you have no backing on this claim ,please tell me what studies you are referring to here and what groups are highlighted in the studies.
If you just look at malayali actors male ,many of them are tall dulqur is 5'9 tovino 5'10 mamooty is 5'11 babu anthony 6'3 (there are 2 actors called this and they are both that height) ,suresh gopi 6'1, prithviraj 5'11,lal 6'3 ,captain raju 6'3,jayram 6'. If you compare heights of famous bollywood actors and mallu actors ,mallu actors are taller .Many of the actors i named are from older generations and they arent new comers either .
In England 80% mallu boys i know that are around the age of 18 is 5'9 and above .This data is reflective of kerala .Im 5'10 and when i go to kerala i dont feel specially tall at all ,my father is 5'11 ,my sisters all are 5'5 or 5'8,my brother in laws are 6'1 5'10 and 5'7.