Check Airman, that sounds like the Boeingization of Airbus procedures. There is no other reason for linking GD with F3.
It is. My company used the vanilla Airbus SOPs until we were bought by another which had both types and where the Boeing fleet was the legacy fleet and had primacy. Now we have had to go back to Airbus SOPs, selecting flap 3 after the gear is down is back in - although I do seem to fly with a number of pilots who haven't noticed. And there is a good reason for it. Airbus don't want the hydraulic systems overloaded as hydraulic pressure is used to both raise and lower the gear. Boeings on the other hand use gravity to lower the gear and the weight of the gear pushing the fluid out of the jack actually increases hydraulic system performance.