Thanks for the advice.

I've updated the Kata to use a List of Tuples in the form (int, int, int).

Thanks, I've updated it.

Yes, you're completely correct. In this case, because there are no triangles in the centre, ALL of the points are external, so the correct answer would be

{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

The diagram should have an edge between 4 and 7, so that there's no hole in the middle.
I'll make sure to fix the diagram. Also, just to clarify, no triangles given will ever intersect.