Censuring people for speculating on 'Professional Pilots Rumour Network' is a bit crass, if you don't like it, then don't log in - simples.
If we were going to have no opinion on why these things happen - then there would be no point in posting them.
If you YouTube "C17 Elmendorf 'aerobatics'" or some such title. Watch that (practice for last year apparently) then theorise away. THAT'S WHAT THIS SITE IS - RUMOURS - fill your boots.
Cranking on that degree of bank, with that pitch angle whilst at low speed would be exploring the stall envelope rather well - even modern fly-by-wire aircraft have to obey the laws of basic physics.