While they certainly believe that God wanted them to win and arranged that they would, I believe that "superior material capabilities" here refers to military infrastructure, weaponry, etc. and they are correct that there are many other factors to the outcome of a war that are compatible with historical materialism and, minimally, part of what is being referred to.

Take for example the social circumstances of the Iranian people being broadly united in an existential struggle against an invader while domestically in the US the war is unpopular and morale is so shit that there are widespread stories of sabotage not on "real" political identical grounds but just because people rightly see the war as them risking their health and lives over literally nothing except maybe a promotion. These are critical to a Marxist account and I don't believe they fit entirely in "material capabilities" in the sense being used here (even if, taking the words in the phrase literally, you could call them that).