Well, the reason that BMW isn't returning his calls right now is that no doubt there is a police investigation into the fire. As soon as an investigation like that is started the lawyers basically put the company in a lockdown mode where they are unable to talk about it to anyone. Basic corporate law; the company I do does the exact same.
There are too many unknowns here to make a judgment about what happened; were there modifications to the car? Recent maintenance? Was there ill-repaired damage from an accident or incident?
While it's possible it could have been a manufacturing defect, depending on the age of the car it's far more likely that something happened after the car was sold that led to this problem. The fact that it had been implied that the car was older (Randy Couture mentioned riding in it several times) I would say either badly repaired damage or a failure of maintenance.
I have seen car fires like this that were caused by someone not tightening down a head bolt properly after a gasket replacement... or failing to properly torque a fuel line. Too many variables to make a judgment... and I don't blame BMW for this at all; they're protecting their interests by refusing to talk about it just like any other corporation would do until the results of the investigation are in.
2001 E46 BMW 330i Sport Package 6MT
2004 BMW R1150GS
2004 E60 BMW 545i Sport 6MT
2012 BMW 135i - Deep Sea Blue / Terracotta / DCT
2012 BMW K1600GT - Vermillion Red Metallic
2008 BMW E90 M3 - Interlagos Blue / Silver / 6MT