But is the definition of the product really just something that has loads of users. If so than the best "product engineers" are just people with gigantic following since every url they share would get traction.

Imo a better distinguisher of demos and products is: "is your thing CAPABLE of solving a real problem" (even if it isn't doing so at a scale atm). Google+ was a product (not a super successfull one), eventhough it didn't have many users. Conversely, a viral interactive gimmick can attract millions of users in a day without really being a product at all.