Did you ask them at the time why they could see it and it wasn't available online? Information they would have provided at the time would likely be more helpful than any speculation here.

As mentioned, this can happen for EXP members as the agents have access to "hidden" inventory that is not available online. That's a documented perk. For non-EXP members, there should not be availability beyond what is shown online. But it's hard to know what actually happened without AA's interpretation at the time.

Cheers.