GM claims the LG Chem cells made in their US battery plant use a different internal separator.  This could be  the factor for a lower incidence of fires but it's not zero.  The new Bolts have a slightly lower kWh rating.  Same battery but the new 100% is not the old 100%.  The slightly lower top off voltage lessens overheating risk.  

The lowest fire risk chemistry is LFP or lithium iron phosphate but volumetric energy density is 20% lower.  In many use cases cooling is not required as their flame point is so much higher and they self extinguish.

Tesla uses LFP in standard range MIC or made in China cars and will probably soon do the same in the Fremont California factory.   This is because LFP uses no nickel and current production is nickel constrained.  A battery might be 80% nickel by weight and nickel is not cheap.  This is why I think the standard range Model is likely strategically coming back.

LFP has a cycle life 3 to 4 times that of typical "laptop" chemistry or current LG pouch cells.  If the 2011 Leaf had used LFP almost all these cars would still all be at 12 out of 12 bars (probably 85-90%).