The truck turned over or rolled over, but it did it all by itself. So, it's a reflexive verb. "Il s'est retourné." If someone were putting the truck away, it would be "Il a rangé le camion." I don't think "retourner" means to return in English like returning an item to a store (rendre quelque chose au magasin pour un remboursement) or putting an item away.
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