Yes McIntyre standing on the left running board is on high alert as he looks around watching the people on the grassy infield panic and start running.
The lone guy running is running koz Hickey some seconds earlier had fired an auto burst of at least 4 shots of which at least 2 ricocheted throo the area at the end of the grass where the lone runner was standing.
The lone runner is in fact near another guy who is just out of frame on left (also running away from the ricochet area).
The other couple (the guy & his gal) are starting to run koz they have seen that Hickey is toting the AR15 -- & they had heard the frightening auto burst (plus echoes) -- & while running they have seen that Hickey is now looking back directly at them (or at least the guy can see Hickey looking back)(i dont think that she did).
Hickey was merely looking back checking to see whether, if in addition to accidentally blowing JFK's head off, he has caused any other damage.
McIntyre is unlikely to be on high alert -- we can see in Bell that McIntyre reaches with his left hand to his mouth -- he grabs some chewing gum -- & throws it away to his left -- he could have of course merely spat it out.
Earlier, McIntyre was looking back/across at Hickey when Hickey fired his AR15 (at say Z300 to Z312) -- after which McIntyre got whiplash when he looked forward to see what damage Hickey had dunn (all of which can be seen in the Bronson footage).
Re Hickey toting his AR15 -- we can see in my gif of Bell that Hickey is toting his AR15 from the first frame of my gif -- he picked the AR15 up from the floor soon after Z219 (ie soon after Oswald had fired his shot-2)(ie his final shot)(his shot-1 had been at Z113).
