I know enough about this to be dangerous but it sounds to me in this particular case the piece that you wanted, the store that had it was likely not willing to do a 1 for 1 trade to allow for that item to be transferred to your store's inventory, then for your SA to sell it to you that way. Some stores will not be receptive to trade/transfer if they know they can sell the item to their clientele with no issue or if it is a high demand item.
I have had situations where I have purchased fine jewelry, my store conducted a worldwide search and the item was found, but transferred to my store's inventory where my SA then sold it to me. I am assuming in this case they sent a similar piece of jewelry to this other store in return. I have also had situations where they find the item I want (fine jewelry or no) and my SA states that the store does not want to transfer but they'll allow me to buy it from them and they'll ship it to me. I've found this happens the most often with the Madison store here in the USA in my experience. Unless it's an item I would literally die without, I usually wait for my SA to source something similar. This happened with a scarf I wanted earlier this season, and I opted to just wait a bit longer because shipments were delayed but my store had ordered it. It took a couple of extra months, but I got it.
The only other thing I could think of is if you are a newer client at your store, your store might could have a policy to not initiate store-to-store transfers until you are a bit more tenured. I know that mine would not transfer anything for me until after I got my first quota bag and generally encouraged me to buy out of their store inventory. It is a lot of work for them to do the store transfer and can put your SA in a tough spot if you back out of purchasing the item for any reason.