No denying that could be, but nobody has been able to replicate it. Why?
Isn't it more possible that as SIG asserts (and they're doing a POOR job with this, PR/response wise), that some string, loop or other thing is in the holster and as they move/lean/walk, that thing pulls and activates the trigger? Especially since this seems to happen with light-bearing guns where the gap to the trigger guard is wider?
That's still not acceptable - and I agree it indicates a series of problems including the nature of the P320 trigger without a trigger safety and being lighter/shorter than other similar guns - but I haven't seen a single instance of anyone being able to replicate a gun going off with zero trigger pull... and I wonder if the straight vs curved trigger geometry makes one or other easier to be accidentally engaged by FOD.