This is just a meme. They couldn't shoot down a plane at any speed.
Shooting down planes is a problem that only one navy solved.
Actually they can shoot planes down however that is if the plane is flying at a certain speed. Now the Germans had assumed that British carrier planes would up to the level of their land based counterparts both British and German. Hence their fire control computers were given a minimum speed limit for their calculations because seriously there is no plane flying at 10 km/h at the time therefore they were calibrated to calculate firing solutions for planes flying at certain speed and above. This minimum speed limit was much higher the Swordfish's top speed of 230 km/h. Note that just because the Bismarck never destroyed any Swordfishes doesn't mean they all got away scot-free as one plane had 175 reported holes from the 20 mm and 37 mm cannons
It still amuses me, that Swordfish was so slow, that Bismarck's AA's couldn't hit them.
The thing is, the royal navy aircrafts attacked Bismarck under the cover of darkness, there was an overcast at the time as well iirc, so you can count the moonlight off or you could say it was pitch black at the time. Hell, they even attacked one of their own cruisers! Just imagine shooting at something you can't see.
