I would like to know how they even managed this.
Many gunpods are angled upwards to loft the rounds high into the air so they drop back down into the line of sight when they reach the target which might be 1-2km away for ground targets.
Cannon shells can leave the barrel at very high velocities but most cannon rounds are filled with HE which is not very dense like lead or steel, so they tend to be large high drag projectiles that are not particularly heavy so they slow down fast.
A 5.56mm HATO round leaves a rifles muzzle at about 920m/s or about mach 3 but within about 500m of travel the bullet will be travelling at 510m/s and it is a slim aerodynamic shape with a heavy lead core.
A 30mm cannon round or a 20mm cannon round is going to slow down fast too... and being in a gun pod it wont be a subcalibre high velocity round...
So high trajectory for shooting at distant targets on the ground in a steady dive means sometimes an aircraft can easily catch up with the rounds it is firing.
Can be made rather worse with low velocity rounds like the 30mm calibre round of the Apache or a 40mm grenade launcher round which is launched at a low velocity anyway.