My ticket is BA, operated by Iberia, so I assume Iberia's cabin luggage rules apply and not BA's?

Iberia's cabin allowence is max 10kg and your usual cabin sized/dimensions suitcase.

I have a HBO fare, however Iberia have the following message on their cabin baggage allowence landing page
(https://www.iberia.com/gb/luggage/hand-luggage/):

IMPORTANT NOTICE

In the interests of your safety and to reduce movements on board, we recommend that you check in your cabin bag, free of charge, and only board the plane with a small bag or briefcase (not available on Iberia Regional Air Nostrum flights).

So does this mean HBO fares, even if ticketed on BA, will include free upto 10kg checked luggage in a cabin sized bag?