What is the purpose of "Schema Owner"?
A Schema's owner is always a User (or Database Role).  There may be a Schema with the same name as a User, because in very old versions of SQL Server a User and a Schema were the same thing.  So there's still a User called dbo and a Schema called dbo in every database.

A Schema's owner is a User who has full control of the schema, and who will be the default owner of every object added to the schema.  Owning an object suppresses permissions-checking on the object, and plays an important role in Ownership Chains.