Granted that what I've written is not elegant/compact/idiomatic, but just wanted to know if it's so bad that it justifies the weird expression on the interviewer's face?

It's just a very simple, even primitive task, so your code should be equally simple (the KISS principle). If I were hiring someone, anything that's not along the lines of

for ( 1 .. 100 ) {
    if ( ... ) {
        ...
    }
    else {
        ...
    }
}
[download]

wouldn't really be acceptable. It's not a test of programming skills, it's a test of common sense (IMO). I'm afraid your code fails it, and it doesn't even show off your programming chops (for reasons already covered by others).