Military experience doesn't necessarily equate to McGyvering. I did a tour as an Army scout. I can shoot a lot of weapons, use knives and other non pyrotechnic weapons, set-up mines, claymores, use plastic, even creative uses for mortar rounds and grenades, but we were never given training on things like making bombs out of windex and a mars bar

The presence of fuel suggests he wanted to do major damage but did not know how to properly capitalize on it's use. Sadly special operations guys are at high risk for CTE stuff. So it's entirely possible he was living a distorted reality.