SUCKMYMUSCLE - you are right that for it to be a proper deadlift, the weight must start from the ground, but just to clarify, for a competition deadlift, there is no requirement that "the back must remain straight".
I agree though, that from an injury prevention perspective, and well as from a strength building perspective, he should use better form a keep his back staight.
A final comment related to a "proper deadlift" - notice he is also using straps (which is fine for training if you use them correctly). In a contest deadlift, the lift needs to be done without such grip-aids.