Well, in my opinion you were probably lucky with the interviewer. I for instance wouldn’t take anybody on who (and I'm no Human Resources specialist or anything at that, but it's a matter of logic) as you say, had no idea of what of the job entailed. I mean, common sense, who would hire someone who has no idea what he is a candidate for?. The least I would do is read a book or two to not be caught out on basic questions on the job you are going to qualify for. Specially since less than 1% of the candidates actually make it to ATC’s.