I have to assume that player B contacted player A to use his #1 priority to guarantee the player is picked up in exchange for the pick ahead of time. Sneaky, clever, but not collusion unless the pick-player transaction is clearly lopsided.

On the other hand if player A simply used his #1 priority knowing that particular player had value and could net him value in a trade that's simply smart managing, maximizing the value of your WW priority.

Seems like a pretty straightforward series of transactions.