Hi Nicole,
I've been in this situation before. I think what's happening is that, for your particular flight, there weren't (3) tickets left in thr $260 fare bucket. I'm guessing that you would have been able to book 1, or possibly 2, of the adults at the $260 rate. Once that fare bucket is exhausted, you were offered the next lowest rate - $282.
I don't know this for a fact, but someone else here may be able to confirm, but I believe that aa.com's search engine will find the lowest available fare (provided that is your search criteria - which is usually the default) for the number of travelers in the itinerary. So ... since there weren't (3) tickets left in the $260 fare bucket, the search didn't yield that result at all and went to the next lowest available fare of $282. In that fare bucket, AA was willing to sell (3) tickets.
I, for one, would love to see the website improved to include some functionality to alerts me when this is the case ... "we're willing to sell you one ticket at $260, and two tickets at $282."