That’s correct. The flights in question operate into LHR using there four digit IB mainline flight numbers.
The only time that BA have leased a IB aircraft and its crew to operate a BA flight was during S16 season. This was a A320 aircraft and it was used to operate two round trips a day to MAD from LHR. These flights were offered the usual CE & ET products.
Customers on the BA510-BA528 receive the standard IB shorthaul product.