Your Friend does not know what He is talking about.
Secondly..., there is no Federal or State Law regarding Bank Carry.
Banks are just like any other Property..., either they are OK with Open Carry or they tell you to leave. If you do not leave when asked, unless a Higher Manager or Company Headquaters tells you otherwise, then, you risk being Arrested for Criminal Tresspassing. Criminal Tresspassing is codified under AS 11.46.330.
Under Alaska Law, just simply Conceal before you go into The Bank and odds are that no one inside will know that you have a Firearm. That way..., no harm no foul, so to speak. Either way though, Open Carry or Concealed Carry in Banks is Legal.