I don't consider the Hogwarts and similar items to be tinplate. The definition I generally apply, in addition to the way the item is made (materials used), is if it is something from the prewar period or a reproduction of an item from that era. There are some exceptions to that "limitation," but not a whole lot of them.
The way I usually describe it is "I know tinplate when I see it."
A Hogwarts certainly could be made in tinplate, but the current versions don't meet the accepted definition.
