It was the first time that any Indian played the character of an alien on screen and successfully so. This is why; the perfectionist did not have any reference point to prep for his character which has been immensely loved.
While he was getting into the skin of his character, he observed Azad minutely to understand how he reacts to new things around him.
Azad was the only person close to a reference point for his character. He helped him understand reactions better and so he spent a lot of time with him while prepping.
So, while Rajkumar Hirani's PK had huge repeat audience, Aamir's performance was regarded as the strongest performance of his career, which says a lot.
Azad was one of the first few people who saw the film and absolutely loved it.