I think marksman have bow mastery.
Again, he was wearing a Short Bow even with Bow Mastery the maximum range with Quick Shot should be 6.
Quick shot have 6 range, Aimed shot 7 and Bow Mastery add +1 range to all attacks.
I am not genius at math but I think that mean Quick shot from Short bow should have 7 ranged if shooter have Bow Mastery.
But it can be infamous PERSONAL BIAS.