Before I answer your question, the pedant in me would like to point out that Ark Royal's Swordfish aircraft didn't sink Bismarck. They merely disabled her rudder, allowing the British battleships Rodney and King George V and their supporting cruisers and destroyers to catch her and sink her.

Now that's out of the way, this is a commonly repeated story about the attack. Unfortunately, I can't find any evidence for it. Admiral Tovey's after action report states that

The torpedo attacks had therefore to be made by sub-flights or pairs of aircraft over a long period in the face of intense and accurate fire; they were pressed home with a gallantry and determination which cannot be praised too highly.

Similarly, the after action report of Lt Cdr Esmonde, who led a raid of Swordfish from HMS Victorious' 825 Squadron reported "very vigorous and accurate" anti-aircraft fire. His raid scored a single hit, but caused very little damage. The Swordfish from Ark Royal had a similar experience - an aircraft from 820 Squadron, flown by Sub-Lieutenant F. A. Swanton, counted no less than 175 shell holes in it. Both the pilot and gunner/radio operator were wounded, while its observer survived the experience unharmed. Several aircraft were forced to release earlier than they wanted to, or to jettison their torpedoes and retreat, by the heavy fire.

In addition, the German war diary does not mention any issues with aiming due to the speed or low altitude of attack of the British aircraft. Instead, it makes massively optimistic claims about aircraft shot down. It describes the attack by Victorious' aircraft as

Thereupon, a renewed attack of aircraft commenced during which "Bismarck" was attacked from all sides. The entire array of calibers, including the heavy artillery, participated in the defense which was made difficult by the zig-zag course and the torpedo evasion maneuvers... A total of 5 aircraft were shot down by anti-aircraft defense, one each by the heavy artillery and intermediate artillery. As can be further ascertained from the testimony of the survivors, the air attack was performed with great daring. In part, the aircraft flew in closely to the "Bismarck" after dropping their torpedoes, and only then pulled up.

While that of Ark Royal's aircraft was described as

A short time later, 35 aircraft dove through the clouds and flew toward "Bismarck" in a daring attack. The entire ship's defenses, including the heavy and intermediate artillery went into action; it was said that 7 of the attacking enemy planes were shot down. During the attack, 2 strong shocks were felt in the ship that had been caused by 2 torpedo hits

While the German war diary is somewhat lacking, being based on accounts from five survivors, it is likely that issues with inaccuracy of Bismarck's AAA fire would have been reported. In addition, this is corroborated by reports made by captured German sailors -

Prisoners state that a tremendous 'Flak' barrage was put up, guns being fired until red hot. According to one man, up to 50,000 rounds of light and heavy 'Flak' ammunition were expended.

From these reports, and those of the British, it can be concluded that the Bismarck had no trouble aiming at the FAA aircraft attacking her.

Sources:

ADM 234/509: Sinking of the 'Bismarck', 27 May 1941: Official Despatches, Jack Tovey, Admiralty, 1941, digitised at http://www.hmshood.org.uk/reference/official/adm234/adm234-509tovey.htm

The Fleet Air Arm Handbook 1939-1945, David Wragg, Sutton Publishing, 2003

Kriegstagebuch des Schlachtshiffes Bismarck, Kriegsmarine Office of Naval Operations, 1941, translated by Ulrich H. Rudofsky

ADM 267/137: Bismarck Survivor Reports, various, Admiralty, 1941

The Swordfishes didn't sink the Bismarck. However, one of them did jam the ship's rudder so it could only maneuver in a circle, which in effect doomed the ship, enabling other British ships to finish the work.

There are a number of reasons why the Swordfish were successful. The Bismarck was taking heavy evasive action at the time of the attack, with gunners working on a rolling and pitching deck. Too, the hit that jammed the ship's rudder also jammed the ship's steering gear into a 15-degree list to port. This, added to the Swordfish's slow speed, made effective anti-aircraft fire difficult but not impossible.

There is one recorded instance of a Swordfish being hit 175 times during the Bismarck attack but flying safely back to the Ark Royal. In this case, the Swordfish's fabric covering meant that some shells simply passed right through the plane without causing major damage.

The Swordfish was also highly successful in the attack on the Italian fleet at Taranto in November 1940.