Social engineering applies to pretty much everything. It has nothing to do with Bitcoin (or whatever else a social engineer wants from you) and everything with your own lack of due diligence and gullibility.
Semantics. Obviously, theoretically, everybody can be fooled. The common sense definition of secure is not "secure with zero possibility of the security being broken". Storing diamonds in a safe at the bank is secure. Printing your private key and storing it at the bank is not any less secure than storing diamonds there.