I'll add the BA flies to many countries apart from USA, and codeshares with many airlines apart from AA. The AA system works more clearly on those few 3 class services it does operate, in which case you'd be sat in AA Business and earning 40/140 TPs there too; but you are codesharing here, and therefore earning at the business class level. Absenting a business class on AA, you're sat in First, but earning the business class TPs.

You can codeshare and get the First tier points - you merely need to book (and pay for) a First class ticket.