Maybe these obvious moves weren't so obvious at that level.

Sure. And I'm pretty low as amateurs go--what I found surprising was that there were ~6 moves where I thought "obviously play X," and 이 immediately played X in half of them and spent 2 minutes to play X in the other half of them. It wasn't clear to me if 이 was precomputing something he would need later, or was worried about something I wasn't, or so on.

Most of the time I was thinking something like "well, I would play Y, but I'm pretty unconfident that's the right move" and then 이 or AlphaGo play something that are retrospectively superior to Y, or I was thinking something like "I have only the vaguest sense of what to do in this situation." So I guess I'm pretty well-calibrated, even if my skill isn't that great.