Nate was using the Sah-7B anti-aircraft missile, also known as Arrow-2M.
The Sah-7 was an old missile, a relic from the 60s, while the Sah-7B was an improved model that entered service in the early 70s.
The Sah-7B used passive infrared seeking, which wasn't very effective for head-on attacks against fighter jets. However, it was somewhat effective when it locked onto tail nozzles of the engines for tail-chase attacks.
After the Mirage 5 flew over Nate's head, the missile's passive infrared seeker head locked onto the tail nozzle of the Mirage 5, the missile launcher began making continuous noises, and then, Nate pulled the trigger.
A sharp hiss followed, then a flash of fire disappeared and immediately a dark shadow shot into the sky, trailing the already departed Mirage 5 fighter jet.