You're auto-attendant is doing a SUPERVISED transfer. It's waiting to see if there's an answer, then pulling back, and putting the call into your voice mailbox. The auto attendant has no idea where the call is ringing. It doesn't care. It's just waiting for the timer to expire, before doing it's job.
If the auto-attendant was doing an UNsupervised transfer, there'd be no way for it to bring the call back.
You're mixing apples, and coconuts, when you're talking about transfers and forwarding.
