You asked what the differences are in something that might be seen on the videotape, that we might interpret differently. The obvious one is movement, which we might interpret as swimming reflex, and which they interpret as an animal being skinned alive.
But there is another point that's really important, and it's part of the training. Certainly sealers who have been sealing for a long time know this, but because of the competitiveness of the hunt and how lucrative it is these days, there are a lot of new sealers getting into the business. When seals are struck but are not unconscious, they have not been struck properly, and they can be in a state of fear-induced paralysis, in which they become stiff and contracted. They actually hold still. So if we see a seal being dragged by a hook, and it's all huddled up like this in the video, then we're concerned that the seal is not actually unconscious.
Again, it's a question of training and education.