There's certainly a lot of info and videos coming out at the moment. When I think back to my first attempts at takeaway cooking, some thirty years ago information like this just did not exist,chefs were so secretive and actually getting into a kitchen was impossible.
I have no idea if this guy is a genuine BIR chef, however his tomato puree and pre cooked onions method is exactly how my local chef prepares his. I watched him cook the tomato puree once, I initially thought the tub I had seen was some sort of massala sauce,but for some reason he cooks it. I'm guessing it's another level of flavour and he hasn't got to wait to cook the tomato puree out on a busy service.
Same goes for the pre cooked onions. When I first starting visiting the kitchen they had a large tub of 'raw service' onions. Next time I went they had cooked them, the Chef simply explained that they were so busy they couldn't keep up cooking dishes waiting for the raw onions to cook.