Hello Azm
Yes, you are correct. The filtering that takes place is filtering of routes from entering the routing table. The filtering does not occur at the interface, but at the mechanism of adding routes to the routing table. Rene mentions the following in the lesson:
Since the LSDB within the area has to be the same we can’t filter LSAs within the area, we can however filter routes from entering the routing table. Filtering LSAs between areas on an ABR or ASBR is no problem.
So it is a matter of the definition of the word filter. Filtering in this case does not occur at the interface, but at the entering of routes in the routing table.
Filtering at the interface however, can occur between OSPF areas.
I hope this has been helpful!
Laz