Imho, that rifle is a poor design. There was no way for it to fail "safely".
Granted that it's possible that no .50 cal rifle could have survived that round.
His earlier shot going wide makes me think the sabot disintegrating in the barrel may have caused an obstruction.
I would be curious to see a closer look at the barrel and to see if it was a failure of the sabot or powder degradation or a combination of both that caused the detonation.
Ian McCollum did a video a while back about the crappy 8mm Turkish ammo that was going around a few years back showing how
this ammo had gotten hotter with age.
https://www.youtube.com/watch?v=AunvMjcJPHY
I bought some of that ammo back about 10 years ago and I can confirm his findings.
About half the ammo was duds and the rounds that did fire were noticeably hotter than what I was used to.