The quote is designed to make you understand that building products is about understanding problems, not listening to desired solutions.
A PM's job is to be the owner of the "problem space", while the engineering teams job is to be the owners of the "solution space".
Fords point was that his customers would only ever tell him about solutions they wanted (faster horse). When in actual fact what mattered to Ford was the problem (current modes of personal transport being expensive, unreliable, uncomfortable, slow, single-person).
Any good PM should be able to explain this to you. OP has never worked with a proper PM apparently... Just BA's and Project Managers that wanted a pay bump.
