Agree with Archchairflyer here. There but for the grace of God.......
Don't forget that the camera is mounted on the RIGHT side of the cockpit (in fact you can see it - a GoPro - very briefly towards the end of the long video), so from the left seat the Husky would have been almost invisible - a small dot right into the sun against a glistering sea surface which then most likely slipped beneath the cowling and out of view.
Also, the photographer on the right obviously was focussed on the Cub, that's what he was reporting on after all. No surprise that he didn't call out. The only one who should perhaps have had a good view of the Husky might have been the Cub pilot.
As I said in an earlier post, I think the collision wouldn't have happened if the the Cessna had continued straight and level, but for whatever reason (better view?), it descended a bit - right on to the wing of the Husky.
I'm not sure if better briefing on the ground would have helped much either, as in my understanding the two banner towers took off from different airports.
The holes in the cheese really lined up in this one, good they all lived to tell the tale.