This is pretty standard for a BAH booking. You can often get a hotel or car effectively for free. I always look at what I can get via BAH when looking at booking flights.even a single night in a hotel booked at the same time ie creating a BAH booking often reduces the price of the fare alone.

There is a downside in that if there are changes to the flights you have to contact BAH rather than BA. You will not usually be able to make changes via MMB.