Preface this by saying that I have no knowledge of this particular accident, other than watching the video.
If my uninformed opinion mattered, I would say there was a loading or C of G factor in the crash. Of the dozen or so types of float equipped aircraft I have flown, the Beaver has to be the easiest to get off the water, as long as it is correctly loaded.
I did many hours of flight evaluation, a number of years ago, for the STC design approval of the modification of the Beaver to move the engine 9.75" further forward, to reduce the chances of aft C of G loading errors, particularly on floats. The modification was a remarkable success. It has been proposed that the original DHC Beaver design was planned to use a "Gypsy" series engine, whose length made the engine C of G further forward. A change to the Beaver's design resulted in the radial being used instead, and the affect was a more aft C of G than perhaps originally planned. The aircraft still flew well, but mis loading aft was more possible.
Over the years, cabin changes by STC provided more space aft in the cabin (evidenced by the changed rear window on the subject aircraft), which further enabled aft loading.
Once you get the C of G far enough aft on a float plane, pushing over to get on the step is really challenging. While nose high in displacement, turning is not so easy. Once on the step, changing the direction of the takeoff run is easier. It looks like lots of space was available, the pilot just could not get the aircraft aligned before he ran out of space. There are probably many factors which made this takeoff not work out, the best we can do is learn, so we don't do it our selves(I came close once, to doing just the same thing in a 185, and I don't forget!)