I'd say they were feral ghouls. Randall was a wanderer running into the Fallout universe as we know it. Ghouls are pretty solidly rooted in the Fallout mythos, so it makes more sense to encounter them. I'm thinking the Spore Carriers weren't around until later, after Randall died of the fungal infection and spread the spores.
Randall probably wasn't killed by the fungal infection as he died decades after he drove out the Vault 22 survivors. People killed by it reanimate as Spore Carriers, his body is right where he died and there are no spore creatures where he dies. They seem thickest where the Vault 22 Expedition camped, at the guard camp and the other place where they penned up the Mexicans then ate them.