99% of the time I travel internationally, it is for business. I always so state on my form, and usually I get asked a question or two along the lines of "what countries did you visit" (though it is right there on the form) and sometimes - what is your line of work. Always asked matter-of-fact-ly, and always my answer is followed by "Welcome Back".

Interestingly, when I returned to the US 2 weeks ago, I got a trainee who was being watched by a supervisor. I overheard the supervisor tell the trainee to be sure to ask questions in order to hear their voices. (my emphasis). So maybe the questions themselves are totally irrelevant.

On the same vein, when I crossed the Russian border by car into Finland, my colleagues told me a similar story - the Finnish border guards ask a few questions of all Finnish passport holders to make sure that they can speak Finnish well since there apparently are a lot of Russians trying to enter Finland on fake passports....