Hmmm
Could he have let the CT filled up with flumes from the fuel cans and then the guns could have set it off?
Or maybe something as simple as lit a fuse then bang
Lots of things
could have happened, I guess.
Without getting too tinfoil-y, I find it stretches credibility that an E8 in 10th SFG and spent his whole career operational in the SF, and that wanted to make a VBIED, made that particular VBIED. Something is very weird in Vegas. Again*
*IDGAF how many news anchors want to opine on echos bouncing around the Strip, I know what an M240 sounds like.