Simon, when he found the others, discovered a near-Utopia for zombie kind. Miles of grazing space, upon which other zombies munched on cattle. There were no uninfected humans to be seen, and therefore, no human brains. Cows tasted much the same, as far as those zombies were concerned. So life there was good.
He had at first approached the other zombies with caution, but the others turned out to be amicable enough. Honestly, they probably didn't notice the new arrival. And when at last the scattered individuals convened back into a swarm, it was doubtful that they realized the extra presence in their midst. Zombies, as a horde, are not individualists.
Zombies may rove together, but even then it's only aimlessly. After licking up some gore hanging from a cow's abandoned carcass, Simon found himself in the center of a horde. No one paid him much attention, but it was nice to be surrounded by people who understood what he'd been through that day -not that their zombieism was actually discussed.