Flap 3 is more fuel and noise efficient so is the default flap unless it would result in extra brake wear, or the IFLD suggests flap full, or there is a tailwind etc.
Also the BA SOP is for “green ops”, ie delaying the drag as long as possible (subject to the 1000 RA stability requirement (speed/slope/config)), plus single engine taxi in/out and minimal APU use.
Plus BA has the -6DB noise suppressors fitted to the entire fleet as per a previous post.
HTH
LD