Did you ask him the question in an open ended way, or did you suggest certain answers? I have a hard time believing they wouldn't have even mentioned at least one of the names in my post if you just asked an open ended question.
This is a rough transcript of the conversation:
Me: So who do you think is the most famous person in the entire world?
Coworker: Hmmmm. Maybe Bill Gates.
His Mentor: Yes, Bill Gates is really famous. Who were you thinking about?
Me: Well other people and I were thinking maybe leaders like Obama...
Coworker: I'm not so sure. Not many people get into politics...
His Mentor: But the US President does have an impact world wide.
Me: What about the Queen or the Pope or Dalai Lama?
Coworker: No. Nobody knows who the Queen is.
His Mentor: Yeah.
Me: Then some people where saying Messi...
Coworker: Well he is pretty famous, but football isn't really as popular in India as everywhere else.
His Mentor: Yeah, I'm not too sure about that.
They do live most of their lives in India. This is his first time in the US. First experience with the culture and everything. But also keep in mind that these are IT workers, so they do have access to the internet a lot.