Attack hits

[Scrapper1]

My partner and I were talking pre-match about a play he had, in which the Libero used an overhand set in the attack zone, but the hit that sent the ball over the net was below the height of the net.

"So not an illegal attack", I said.

"Not an attack at all, since it's below the height of the net", he replied.

Now, I fully admit that I'm not as good with volleyball rules as I am with basketball rules. But I thought that any hit -- other than a block or serve -- that passed completely across the plane of the net was an attack hit.

Am I wrong on that? If it goes outside the antenna, is it still an attack hit?