Naaa.  It's going to be the Pole version of it, if not UK.  
it's a UK version. I saw an interview with a guy they hired to make sure it's historical. he said it was americanized initially - for example - "ok" wasn't used in UK in conversations until 60s apparently. 
As for explosion, it looks weird. Then again, i haven't seen 20mm exploding on a plane. If I remember correctly 109E shell was a MG FF/M shell that carried 3x explosives of normal 20mm. 
I doubt that i can ever watch a wwii movie without getting into some detail of it. Can you imagine this: 
- 109 tracers were too often - usual load out was xxxx
- spitfire turned too tightly, you can see it dive earlier it would have to overshoot and it didn't.... 
- p38 dived steeply but you can tell from markings that it is an early model and he wouldn't pull out of the dive !!!
