My Indian friend said he was an Aryan and according to the Aryan invasion theory this is most likely true, but would an Indian from Northern India (Like my friend) be considered an Aryan in the Nazi definition of the word?
Your friend's claims are rooted in 19th century theories which have been discredited. The term "Arya" merely means honorable/noble and is not a racial or ethnic qualifier. It was coopted in the mid 19th century by proponents of antisemitic and master-race theories. In India, the British colonial government endorsed and propagated this idea and retrofitted it onto the caste system. It gave them a convenient narrative of white Europeans as high-caste, and helped them make allies of high-caste Hindus. Your friend, unfortunately, is one of many Indians who still subscribe to these discredited ideas.