what he says makes sense
but lets remember that prior to the events on halo 1 the SPARTANs armors were different,
i dont rememer exactly how much but was about a few days before the fall of reach and the events in halo that the spartans got the mjolnir with shields(the one from halo 1) this is revealed in "the fall of reach"
so maybe this armors are the ones that they had, before shields were added
we may even se master chief in this game