False dichotomy, it's evidence for both. One conclusion might be false and the other true but other arguments are required for you to get to that point.

Yes, it is probably evidence for both, depending somewhat on what people's beliefs are about how those in the subset likely differ from the others in the superset with regards to relative response to interventions.

However, I wouldn't say Alicorn was presenting a dichotomy. Sure, I would have said "that doesn't necessarily mean" in the first case and "but it does mean" in the second just for extra specificity but I wouldn't say that is required.