That sounds like a one-off on the fares side, usually Basic fares are discounted by around $100 to $200 area over standard tickets, it's certainly a good reminder to not automatically ignore Basic fares.

The key rules are found at the end of this thread (see table):
https://www.flyertalk.com/forum/brit...announced.html

You will be paying BA on the outbound, and AA on the inbound. Essentially the rules are in the table as to whether you actually get a free bag or not (on BA = not) and the operating airline charges the fee. The fee should be the same between all the JBA airlines, at least for the first bag, and would be $55 online $60 at the airport. That is each way but includes the shorter connecting hop to DUB.