It probably had to do with the reporter assuming that, because the reporter possibly liked American Football, that everybody else would like it too sort of question.
If you had a son, of Olympic caliber who had won a gold in London, who was asked by an English reporter if he intended to sign up for the national sport of Cricket, what sort of response would your son give?
Probably a similar response Usain gave to the reporter. :)
If I had son he’d be way too young for the Olympics. ;-D
If I was an Olympian and asked such a question I’d be flattered that someone thought I could compete in a different sport.