I think it's just to show us the other meaning of "acțiune"? As a translation for stockbroker I only found "agent de bursă" or "agent de schimb". "acționar" = shareholder.
It has nothing to do with economy here. This expression just means "man of action".
If 'acțiune' also means shares why in this case dose 'om de acțiune' not mean stock broker?
If it really means a man of action there is little point in it being in this lesson on economics. So I am sure it must mean stockbroker too.