I saw that, but didn't pay much attention because I really don't think 12 weeks tells you anything.
I would say if you take any meat eater and make them vegan for 12 weeks, almost everyone is going to see improvement in basic health indicators, like the one twin saw. The question is what happens if they keep that up for 10 or 20 or 50 years? It takes a long time for things like B12 or iron or zinc deficiencies to show up.