Australia's physical connection with the mainland of Asia disappeared 4,000 years ago. It is assumed that people from India crossed into Australia before this time. There is little proof of this. Indians and Australian Aboriginals are distinctly different. Aboriginals are more like Africans, while Indians appear to be black Caucasians.
DNA tests on both gene pools do show a link. However, this link could be directly from Africa 70,000 years ago. A similar thing could be said about Neanderthal genes being carried by some modern humans. The markers could have been there before both species split off from a common ancestor. The fact that Neanderthals have a different number of chromosomes is dismissed by some scientists when it is known that offspring of related species with differing chromosomes can have offspring but they are invariably "mules" who have infertile young.
Australian Aboriginals are the earliest of Mankind to leave Africa. There were many waves of movement out of Africa. Southeast Asia is much closer to Australia than India. When Europeans first arrived in Queensland there were two types of Aboriginals, One very dark skinned with robust features like natives of New Guinea, and a lighter skinned more gracile kind.
India is divided socially today into very dark skinned people who have been in the country for a large period of time, probably those left behind on the Aboriginal migration to Australia, and lighter skinned Indians who arrived more recently. There may not have been later interaction from those who remained in India on the very first journey from Africa and Australian Aboriginals..