My guess.
1. Guard responds to whatever shooting occurs from buyers to Paddock (Paddock dead).
2. Guard retreats, buyers fire into crowd to cause confusion and shut down the strip.
3. Cops bumble around until SWAT shows up, they go in and are fooled by fake suicide.
How about this possibility?
So-called hero guard is part of conspiracy. He takes one from the team and then takes no further action until he hears the shooting stop.
That gives the conspirators time to get away. Paddock is left for dead.
The “hero guard” plays out his role as long as possible then disappears, either by stealth to meet his handlers, or because they see he is a liability (although they want to take credit so why would any evidence pointing to them be suppressed by them?)
Paddock could have been a willing conspirator and done some of the shooting but with two broken windows, you have to wonder if there weren’t one or two other men in the suite, and also, there’s the slight chance that Paddock was never in on the plan, although he brought in the guns for some unrelated reason such as a clandestine gun show for what he had been told would be arrivals the next day. Thinking the conspirators were an advance set-up team, he welcomed them in and got shot? Possible. Anything’s possible if the security guard isn’t saying everything he actually saw, or if he deliberately ignored some events.
Obviously his wounds were rather superficial compared to what one might expect if a maniac unloaded 200 shots at him through a door, but then if that all happened a minute later and one convenient flesh wound was administered before he got out of the way, then no mysteries. It does seem a bit contrived to involve this dude at all, most of what I described would have been easier to do without him around at all. So maybe he was an instant recruit. (hey brother, don’t ask questions and roll up your pant leg).