Yes there are Flak-like light flashes and impacts all over the place in the OT. While I can believe that a Stardestroyer, the Death Star or an AT-AT might be armed with flak-cannons to shoot down smaller ships (That's what flak is for) I'm not sure I buy a small Snowspeeder being armed with flak-cannons. Why would a fighter be armed with two anti-aircraft weapons?

So I still suspect that flash is just too high due to a mistake with the compositing. But if it doesn't bother anyone else and more importantly if it doesn't bother you Adywan, then it doesn't really matter.