Then again, if a "video view" is defined as "watched over 3 seconds (50% of the video visible in the screen, IIRC)", then it sort of makes sense that "Average Duration of Video Viewed" doesn't include non-views.

For sure Facebook should attempt to name their metrics as descriptively as possible, but also advertisers should make sure they understand how different conversions are measured, what's included and what's not. Another example would be "Clicks" metric, which included all engagement (i.e. likes, shares etc), instead of just "Link clicks".