Nothing to do with BA, it’s just aerodynamics.

When a fixed wing aircraft gets close to the ground (less than a winglength - maybe about a quarter winglength for a noticible effect) then additional lift is generated from the uplift of air passing under the wing. At this time it’s possible for the plane to fly at slightly lower airspeed than would be normally required to maintain lift.

Ground effect happens on take off as well as landing, it’s not as noticible though on take off (unless you’re the pilot and try to rotate before you’re at the right airspeed!).

This effect is sometimes used in actual water skimming craft.