Word or expression for comments that are technically correct but unhelpful [duplicate]

Consider using tangential or peripheral.

If you're thinking specifically of getting replies that are about grammar or formatting when you're looking for something about actual content or algorithms, I'd say "pedantic".

pe·dan·tic (p-dntk) adj. Characterized by a narrow, often ostentatious concern for book learning and formal rules

If that was just an example and you're thinking in broader terms, JasperLoy's suggestion of "tangential" might be better.

While it is neutral as to the correctness of the answer, inane focuses on its lack of usefulness

extremely silly or lacking real meaning or importance: There are so many inane programs on television!

And on computers!

Similarly, irrelevant and immaterial.