To say that you are interesting means that you hold the interest or the attention of someone. Typically it is a good thing here in the US.

"why did the interviewer say i am an 'interesting guy?'" in the states, when we say something is "interesting" we are being polite. maybe he's just being nice. :P however, he could have been literally meaning you are interesting to him and you stand out amongst the other candidates, eh?

Hello Gogo, He probably found something interesting about you .What he meant exactly no one can know but him or you maybe. It depends on how he said it too ,was it a sarcastic tone or did he seem fond of you ? It is difficult for anyone who doesn't know you nor did attend this interview to answer this question. Why didn't you ask him directly why he finds you interesting?So if you are going to have a second interview with him or somehow you are getting the job just remember to ask him :)