Regardless, dollar for dollar, if people are seeing bigger conversions or returns it doesn't matter whether they came from display advertising or 'organic content'.
If someone is intentionally adding correlations using predictive information then they are stealing money you did not have to spend on traffic that was inevitable. It is like standing inside your waiting room to hand out your buisiness cards then claiming the sales commission.
If you have independent metrics of your own spend, then no, facebook didn't tell you. But you'd have had to have had similar spends in similar ways with all their competitors to know that.
If they buy something, who cares?