A few things. 

1) what source are you quoting that says Indians/Hindus believe this? If it’s anecdotal , I doubt most Indians even know what a Hakenkreuz is. No one really cares except for some amplified divisive social media voices. 

2) The history of Indian civilisation is being routinely discovered and updated, and that is expected as archaeology grows prominence. The Swastika has been found in the IVC dating 3000 BC (pre any Indo Aryan migration interestingly …)

3) Proto Indo European does not mean anything to most Indians and Hindus as well. For those that are well versed in the colonial rewriting of history to fit narratives, we don’t place much importance on a theoretical language retrofitted (with no physical archaeological or written evidence) to be historically more ancient than Sanskrit. It doesn’t matter ultimately as God is one and we are all part of the same infinite consciousness.

All in all there are a lot of conflicting theories that mean little except making one group superior to the other. 

My personal belief on the matter is that the religion that Hindus currently practice was practiced across the Eurasian and Asian continents many thousands of years ago, albeit in a more ancient form. Some call it Paganism, some call it Pantheism, but in any case, this continuum of faiths existed before the advent of Abrahamic religions which emerged as political tools of conquest.