I agree. It is weird, and I can't decide if that is just a coincidence or an artifact of the stitching process.
Additional: I just looked at the original frames and they do show bands of color, but they don't appear to line up with the tree branches in the same way as shown in the composite.
Additional additional: I just reran the composite -- and made sure that I did not click the "auto-fill-in" function, and got exactly the same result.
Cheers, Jock