Question about a right? semi-join

[westonpace]

The documentation states Right semi join can be used when cardinality of the subquery is greater.. Does a right semi join create a hashtable from the left side (e.g. does it swap the implementation and treat the left side as the build side?)

My guess is that it does. But then this later sentence confuses me:

Right semi filter join returns build-side rows which have at least one match on the probe side.

Is a right semi filter join actually different than a left semi filter join with the inputs swapped?