You mean the bags are snake oil? Not really, Of course they will burn, everything will at some temperature- even flame retardant racing suits. What they do is buy you time, time to get whatever is burning into a safer place, like out of the house.
I don't think the bag manufacturers say in absolute terms that bags won't burn, just that they are resistant.
Yes, LiPo bags are snake oil. Look at videos. Do some research. Unless you are sitting there watching the LiPo charge they do not buy you much time at all. They are a bad invention that creates a false sense of security. Most of the LiPo bags are completely useless.