You can't have oxidation alone, it is a electrochemical process where some other material in contact with the one oxidized has to be reduced. Corrosion of the meteorites equally could occur if these simultaneously contain grains of metals / alloys differing in the their electrode potential provided

• these grains were in close contact with each other, especially if their grain boundary were water wetted, and

• if one of the metals / alloys -- relatively speaking -- would be «less noble», i.e. a material with a more negative reduction potential, than any other grain / material in contact. The less noble grain than would become a galvanic anode and eventually be "eaten away", protecting the other, more noble one, to be oxidized.(table) The formation of these little, local electrochemical cells could be even more important if there were salty water droplets on the surface at room temperature and above accelerating corrosion. (This, by the way, a reason why steel bridges and copper house roofs exposed to the climate and atmosphere of salty seas are more prone to galvanic corrosion than similar constructions only exposed to fresh water.) Presence of phosphates in said meteorites however could slow down the oxidation of the meteorites (passivation, as assumed for the Iron pillar in Dehli).

Note: The initial answer assumed iron meteorites to contain discrete grains, occasionally altogether with grains of other metals. A comment by@KenFabian pointed out iron meteorites however mainly consist of (Fe,Ni) alloys. Their electrochemical properties may be different to their components (e.g, table), which the edit aims to include.