Move 1: Take 4 of the balls and divide them on the scale in 2's. If the scale is balanced, then you know your 5th ball is the heavier one. Move 2: If one side is heavier, then just split those balls up on each side of the scale and you've found your heavy ball.
Most interviews were more of a conversation than a traditional interview or behavioral Q&A. More like, "Let's put a 'live' problem on the table and whiteboard some ideas for how you might approach it."