If you talk to Sig about it they say all cases like this in which any investigation has been allowed at all, show that some piece of foreign material or equipment found it’s way into the holster and manipulated the trigger discharging the gun. (That is if it is not a direct negligent discharge when trigger is pulled by user).
Obviously I don’t know, but that claim makes sense when you look at the changes holster companies have been making to tighten up the body of the holsters to the firearm. The older Safariland holsters had all kinds of slack and wiggle in them compared to newer holsters and also had sealed bottoms where most newer designs have open bottoms.
Regardless, the claim that something pulled the trigger rather than “it just fired on it’s own” makes more sense to me.