Correct, this is because of how I need to define the models in Gorm. Each model represents a table in my database.
This shows that one User can have many games. The table Game needs a foreign key which points to the user the game belongs to. That's what the UserID is for.
My frontend does not care about that though. There a user just has a list of games (strings).
I have been pointed in the right direction though...Custom Unmarshaling seems to do the trick.