I'm confused. (OK, not a rare event.)

The concentric growth rings seem to imply that the bowl was spun about what would be the vertical axis of the trunk section. However, that wouldn't have left bark, if indeed that is what the dark stuff is, around the lip.

To get "bark" on the edge would require turning about what would be the horizontal axis of the trunk section.

Was the "bark" applied after the bowl was turned?