Before going into the main question, I just want to point out that the US Navy had very serious problems with their torpedos during the entire war. This is a good summary of some of the issues:
WWII U.S. Submarine Service Torpedoes
As to the differences in production quality and precision, there seems to be two issues:
1) there was a very big difference in production methods (and to a great degree, ethos) between US and British manufacturing before the war. British production was not as industralised as the US. The US had moved into the Fordist production lines that had initially been created for the mass production of cheap consumer goods. Consumerism hadn't hit Britain before the war.
Whereas the the British production of weapons and equipment was of a very high precision quality it just couldn't match the needs of the war. This is apparant in the problems encountered in the mass production of the Spitfire. Beaverbrook had to take Supermarine to task about it's appaling production record.
The US utilised it's factories that had been turning out cars, fridges etc and used the same assembly lines to produce weapons. This speeded up production and allowed more a greater quantity to be prooduced but the quality standards were variable. One reason was because most of these factories were still run by their existing owners, and US production was as centralised during the war as it was in Britain. Another was that the great demand in workers meant that a lot of untrained people were recruited.
2) Another issue in this particular case is probably that the US manufacturers were never told what it was that they were producing as the weapon was top secret. So their standards would have been based on their own knowledge of standard bombs that didn't require the same standards.