I think you might be slightly misunderstanding the intention of the subway example (1.) - the “market” described is one of commuters for seats, and the example is noting that if some subway seats appear underpriced—i.e. commuters are choosing to cram together in fewer cars rather than equalizing their density over all available subway cars—then those commuters likely know something about the unused seats that you don’t know.
I think you might be slightly misunderstanding the intention of the subway example (1.) - the “market” described is one of commuters for seats, and the example is noting that if some subway seats appear underpriced—i.e. commuters are choosing to cram together in fewer cars rather than equalizing their density over all available subway cars—then those commuters likely know something about the unused seats that you don’t know.