No its not. If you read the article, it very logically explains how caste system was prelevant in Southern India even before any such so called Aryan migration happened. Not to mention that we dont know for sure whether the Aryan migration happened for sure or not, as it hasnt been proven 100%, for all we know it could just be a myth.
Large scale migrations to the subcontinent happened for sure. That can be easily demonstrated by genetic/DNA evidence. What is in doubt today is whether the Vedic civilization was established by those migrants, or whether it was developed indigenously and later adopted by the migrant indo-Aryans.