how can such two 180 degree verdicts even happen?
This isn't so rare, is it? That's what appeals are for.
In this context, the new ruling was not just that there was insufficient evidence but (as I understand it) that she likely had not done it. I don't fully understand the distinction in the Italian system but in the American system at least appeals don't generally do that sort of thing.
See: You Be the Jury, The Amanda Knox Test
While we hear about Bayes' Theorem being under threat in some courts, it is nice to savor the occasional moment of rationality prevailing in the justice system, and of mistakes being corrected.
Congratulations to the Italian court system for successfully saying "Oops!"
Things go wrong in this world quite a bit, as we know. Sometimes it's appropriate to just say "hooray!" when they go right.
Discuss, or celebrate.