Does restoring an Oracle backup of the whole database restore schema objects?
You're issuing a "recover database" command, which will recover the database as far as possible.  If that includes the archivelogs/redo logs which contain your "truncate" command, then this will also be re-played and the table truncated again.

Try doing the restore on it's own, or recovering to a specific time using RECOVER UNTIL... then opening the DB read-only to see if it's in the state you expect.