Yep, that was it. Man, I really misremembered that. It's an Objective-C thing, which makes sense, because it was for an iOS position. I knew the idea behind it, but I had never encountered the term. I do remember I ran into it again while preparing for interviews again a year ago. I'm deep in .NET territory for work and Python for fun right now, so my iOS knowledge has atrophied a bit.
Yep, I lost an interview about ten years ago in part because I had not encountered the magic term "duck typing" yet. Never mind that I had be making file-like and string-io objects in Python for years by that time.
Don't get me started, tech interviewers are so bad...