Quick correction. Iguanodont refers to Iguanodontia, which includes species such as Dryosaurus and Parasaurolophus. What you’re probably thinking of is Iguanodontidae (Iguanodontid), which doesn’t include Ouranosaurus.
Not really. What I said was correct. Iguanodontia is just a more inclusive clade. It includes both hadrosaurs as well as the more basal species we generally label as Iguanodontids. But as far as I know Iguanodontidae is a paraphyletic group and thus has no meaning in taxonomy. So it's just an informal name like some others groups such as lizards or fish which also have no real value in taxonomy.
Ouranosaurus keeps jumping around in the phylogenetic tree. But most recent studies place it at least close to Iguanodon and outside hadrosauridae. Though sometimes it is included inside hadrosauroidea. Since it's exact taxonomic position is a bit unclear it's best to name a more inclusive clade in which it definitely belongs. Which is why I said Iguanodont (as you say, the informal name for Iguanodontia). From Ouranosaurus and Iguanodon to Corythosaurus and Parasaurolophus etc.; all of these are all placed inside Iguanodontia. Some are just more advanced than others.
And since the game doesn't have a complex phylogenetic tree, 'cause lets be honest, that would be too complex for the average player, it's better to simply use this more inclusive clade and say that Ouranosaurus is a basal iguanodont/iguanodontian.