Kingfish wrote:
What is a glider doing up at an oxygen altitude of 16,000ft? Isn't that
a tad close to the Class A?

Flying. What makes you think gliders can't or shouldn't be that high?
We have a word for tad close to the class A, we call it class E airspace
and it ain't reserved for bizjets.

I'll also give you a clue. Gliders can get authorization and do fly
in class A airspace as well.

What we apparently have here (from preliminary data) is a massive
failure of see-and-avoid on the behalf of both parties.