The number of people who know anything of history at all, even history of their own peoples, their own country, their own family, is "very low". Absent of course the "history" that Hollywood and other popular media pumps out.

I think their point is that most peoole aware of the time period know child labour in factories was prominent, especially thanks to Dickens and other authors, so most would guess or be unsurprised to find these cable factories employed children.

What difference does 10 years make when you are working in a shitty factory for peanuts?