It sounds like even if you assume that a chirality change or flavor violation occurred just before the particle would have emerged out of the south pole.

When the problem is considered from a perspective of mass eigenstates, the flavour can change in a distance that's roughly proportional to 2E/|Δm²|where Δm² is a difference between squared masses/mass eigenvalues of transitioning neutrino. If I didn't make a mistake in my back of the envelope calculations, then at those energies it's at an order of tens of meters. EDIT: Scratch the last sentence. I used a bunch of possible values and considering the possible range for masses it's basically a meaningless figure. Sorry!

But when considering your question as a whole, I'm less convinced of my guesses. I only considered what could happen to neutrinos at that energy and what could explain it simply (thus considering neutrinos as Dirac and not Majorana particles). I hadn't yet tried to guesstimate my way through the whole problem.

I'm not a particle guy.

Same here. I'm happy about it.