I am sure linguists would not agree with the writer. Root language of Sanskrit appears to be Avesta, while linguist refer to root language of Tamil as simply proto-Dravidian. For the former we have physical evidence, while for the latter we don't and thus a working hypothesis. Raj Mutharasan
Small correction - the root of Sanskrit is not Avestan, rather Sanskrit and Avestan share a common root that's often called proto-Indo-Aryan. which itself has another postulated root called proto-Indo-European.
Even that's not really true; what we refer to as "Sanskrit" is really Classical Sanskrit, which evolved with Panini et al. Technically, the original languages are the Prakrits, which were refined into Sanskrit. Tamil is one of the sources for that refinement - though to a much lesser extent than the north-Indian prakrits, but it's definitely a source.
Sanskrit can't be the root language of anything except maybe Hindi and (to a lesser extent) Urdu. It's a leaf language, not a root.