Being asked about chopsticks isn't offensive...it's baffling, irritating, odd, and lots of other things....but it isn't offensive.

The reason it's odd is because 90% of the time you get asked this question is outside of dining situations and is therefore not relevant to anything. If it were during a meal, then the message of the question would be "I am asking out of kindness and trying to help you enjoy your meal." But when just asked out of the blue the message is "I consider you an oddity and am asking you questions to safisfy my own morbid curiosity."

I also think it is perfectly fine to strike up a conversation with a random stranger....if you have something to say. Where so many people make their social faux pas is by prefacing their conversation with "Can I practice my English on you?"