Video
I went back and looked at the video from the construction company several times.
To me, it does not look like they were vertical or in a bank.
It appears they were moving fast, and fairly level, which would go along with the comment that they started out high and fast.
We don't know of the VNAV capabilty of this aircraft, so one might assume they were using the "dive and drive" technique.
Just another observation.
RGDS
OBD