Exactly.

A column cannot be present in an index twice. If a column is explicitly specified as part of the index and it is part of the clustered index key, it will be present in the index once. If it's specified as a key column, it will be a key column. If it's specified as an include column then, if the index is non-unique, it will be a key column (which it would have been anyway if it was just implicitly part of the index), otherwise it will be an include column.