Wards and hostages are different. While a ward is a hostage, a hostage is not always a ward. Hostages are exchanged to ensure that one or both parties behave each other during a truce. A ward is raised as if a child by the person keeping them as hostage.
Hence, Theon Greyjoy is a ward, but when hostages are exchanged in season 1 of The Last Kingdom (including the protagonist - Uhtred), it is "only" an exchange of hostages. No-one involved on either side (all of them warriors) can be considered a ward.
So if the hostages being exchanged are already adults (as it seems to be the case here in Forbidden Lands), they would not be considered wards. Hope this makes sense.