The summation in the linked story is "Improper manufacturing, external damage or inefficient or malfunctioning software can cause a lithium-ion battery to catch fire. "lthough there are different reasons why EV batteries catch fire, I just read this article and posted the link above which gives the most likely reason.
The Bolt's issue was determined by GM and LG to be improper manufacturing by LG that resulted in two defects in some batteries. This has been addressed. So now we have two admitted non-experts apparently speculating that there may be a different reason and the problem therefore remains unaddressed despite the recall. This is idle speculation.
I suspect my Bolt never had the defects. Given it's age and how I charged, if it had had the defects I think it would have manifested in those 5 years. The handful of Bolt's that burned were all late model years as I recall.