To be fair, I hadn't really understood "in demand" to mean "actual sales", so I'm sure it is indeed more along the lines of looking at how many "interactions" there are on "the socials" .
That said, there are ways to get a rough idea of sales trends without knowing actual figures, too -- some market research companies even scan email receipts in people's Inboxes, if they're daft enough to give them access to that sort of thing. (Which all too many people are.)