If a Pokémon holding a Choice Scarf Dynamaxes, the item will temporarily have no effect; the stat boost will be disabled, and the Pokémon will no longer be subject to move locks. After the Dynamax ends, the stat boost is restored, and any previous move lock will be re-enabled.
It used a Choice Scarf, outspeeding Calyrex-Shadow with Air Slash. It then Dynamaxed to negate the move lock. Thus, this scenario is completely plausible.