I watched it a bit closer. The smoke starts while descending, the floats pop while climbing again. Quite a bit of time in between. The smoke stopped pretty quickly after regaining a normal attitude. The smoke looks like it is above the tail boom. If that much smoke would be produced by popping the floats, we would never have tested them inside the hangar. My bet is on the engine, not the floats. And one does not need a lot of oil to produce a lot of smoke.
In that situation I can see myself easily popping the floats, just in case.