Question about sirocco

So I played against my friend.
He had sirocco on his field and I had chaos sorccerer.
he used the effect of vayu to special summon armed wing,
then I chained book of moon to retun armed wing facedown.
He said he use priority so before armed wing turn facedown he can use sirroco to take it's atk.
I told him he can't do it because he chained speed spell one (sirocco) to my book of moon which is speed spell 2.

So who's right?

If he is the turn player he has the right to place an effect as a Chain Link 1, so he indeed can use Sirocco's effect then you chain Book of Moon and Sirocco won't get any Attack because he is the only blackwing monster on the field.

Confirm what Train Heartnet said.

If it was his turn than after he had summoned BW-Armed Wing he could have activate Sirroco eff with Priority, to which you could legally chain Book Of Moon. Chain would resolve Backwards and first BW-Armed Wing would be flipped face down and then Sirroco would gain attack from all other monsters that are face-up during resolution...however because Armed Wing was flipped face-down his attack won't add up to Sirroco's