EdgeContinuity is reporting a tangency difference of 0.09 degrees which is what you are seeing with Zebra, The Angle tolerance in DocumentProperties > Units is set to 1.0 in your file and the Tangent tolerance in EdgeContinuity is set to 1 in your screen shot.
If the tangent tolerance is 1 degree and the actual difference from tangent is 0.09 degree then Rhino thinks the surfaces are G1 continuous even when Zebra shows that the surfaces are not exactly tangent. Zebra does not use the angle tolerance. Similar for distance and curvature.
How did you “join” the surfaces? Join did not work for me because the surfaces are further apart then the absolute tolerance. Or did you set the absolute tolerance to larger than 0.09 so that Join would work?
Added: Zebra shows what the geometry is based on the mesh created using the mesh settings. It does not use any tolerance settings.
The discontinuity in zebra stripe shows a discontinuity in tangency. I used MatchSrf with Position matching which results in G0 continuity (edge locations match) but not G1 continuity (tangents do not match). I still see a discontinuity in zerbra stripes which is expected.
I used MatchSrf with Curvature matching and tight tolerances and the zebra stripes are nice and continuous. Settings used were:
Zebra shows a simplified rendering of the reflection on the selected surfaces of a zebra stripped surface. It does not do any calculations of distance, tangency or curvature. It is essentially an EMap of a zebra surface. (This is fundamentally different than commands like CurvatureAnalysis which calculates curvature properties and then displays the results of the calculations in a color code.)
The Zebra mesh is created using vertices on the surfaces being examined. The toleances in the Zebra mesh settings determine the spacing between the vertices. My understanting is the Zebra mesh angle setting determines the maximum angle allowed in the Zebra mesh. Depending on the surface shape and other mesh settings the actual maximum angle in the Zebra mesh may be smaller than the Zebra angle setting. That is probably the situation in your example. Zebra does not use the Rhino document propereties angle tolerance.
What you see using the Zebra command is determined by the orientation of the faces of the Zebra mesh…What you see does not depend directly on any tolerance settings, either for the Zebra mesh, the Rhino render mesh, nor the tolerance settings in Document Properties. It also does not depend on how the surfaces being examined were created.
Because it is possible to see larger deviations from G1 if you look carefully with the Zebra mesh created with the settings your are using.