How Union Transformation is Active transformation ?

Generally, the Union transformation returns same number of rows that passed to the transformation. For example; if source is table 1 contains 10 rows and Table 2 contain 5 rows then the Union transformation behaves like a UNION ALL in SQL and returns 1 records. That is the number of records unchanged which means it is a Passive transformation.

But in the Union transformation properties we have one option IS ACTIVE, when we enable this option it follow active mode. otherwise it will follow Passive mode.