The later case is different than simply updating the DeletedAt column.
The database not actually deleting is still the application properly deleting it. If the DB eventually carries that out or not is a lesser concern to me, tbh.
The concern here is that facebook doesn't actually tombstone their entries or doesn't even have their DB mark it deleted.
(More than just Cassandra tho, many databases don't actually "delete", at least not immediately. They "mark for deletion", and may or may not _actually ever delete_ anything.)