the reaction from the two witnesses standing on the side of the dude pumping something, is what keeps me thinking the shot came from that side. They have an obvious painful reaction to something blown out with violent force and sound, bet their ears still ringing
look at the hand of the dude in white - it recoils from fire right at the 4 sec mark, then the boy to his left grabs his ear, and the girl falls back from blast and grabs ears too