All you can really see is the dust from the collapse of the other two towers. I see maybe, tops, 2 floors with sections that seemed to have had a fire, but nothing that screams inferno at me.
As for the flashes, at this resolution and as I believe I saw on the other topic with this same video, those flashes could be anything. I don't think it could be reflections, with all the dust I doubt any indirect sunlight could do that. I think it was probably something like the hard hats a coal miner might wear. Imagine: The dust is blocking the sunlight, and if I have to plant explosives, I need to see what I am doing because if I haphazardly set the charges, I could screw up the operation. So, it's not too far off to suggest it might be flashes from that type of helmet.
It could also be the firefighters that were supposedly 'pulled' from the building, also, I think they use something similar to penetrate thick smoke. But as others have said, it's just a little too far out to quite see what is going on at this scale.