At 3:31 does it look to others as though the Cub pilot is trying to draw the photographer's attention to the Husky by pointing his finger?
Maybe, indeed.
OTOH that would hardly be an effective and/or unambiguous warning (couldn't such a gesture also be understood as "descend a little"?
). If the Cub pilot really has spotted the Husky and was in radio contact with the Cessna (both pure speculation), then relying on handwaving instead of R/T would seem the gravest and least understandable omission to me
.
Edit: BackPacker's conjecture that there never was a planned formation between Cub and Cessna somehow makes sense to me; in that case cancel gravity and lack of understanding.