Welcome to FT with your first post.
I would guess that the first airline bag allowance was one free bag so you got an additional bag. I am not sure what fare class AE rewards booking books into on the first carrier. Typically the rules enforced are first carrier rules unless you have a longer flight on another carrier (most significant carrier), then those rules apply. There is some grey area in what gets assigned based on ticketing carrier, MSC and first carrier. IMHO.