Yup that's just the normal lag. Everything that you see, especially the shell trajectories, are basically a view into the "past". He shot a tiny moment earlier on his FE, where you were just a few yards behind the place you are on in your film. No bug.
You can see this phenomenom even better when you review your dogfight films. The enemie's bullets just seem to miss you, yet you get damage. But there's nothing fishy in that.
