I would agree..theres a good 20 odd characters in the game so its a matter of us guessing until the right name comes up, plus a few people are non gamesplayers so they would have no idea but ill give it another shot..Bowser?
I think the question is fine, you look online to see what characters there are available in the game, so it doesn't matter if you are a non player.
Also you try to guess the character based on the persons personality and which you think most suits them, like in Mario and Sonic I play as tails because he is so cute!
So I have been looking at Mario Kart on the web and there are actually 8 lightweight characters in total as some are unlockable.