It’s a common misconception that security guards and stewards are the same thing, but there’s a few key distinctions to make. The main one of these is that stewards do not need to have any formal qualifications, whereas security personnel will have been accredited and vetted by the SIA.
There’s also key differences in the duties they can administer. Because of the gulf in the qualifications they have, SIA-licenced guards can complete a much wider range of responsibilities, and take on a more authoritative role than stewards can.