The Klingon sentence said SuSDeq 'oH DIron'e' using singular 'oH but the suggested sentence is plural "The bagpipes are a windbag instrument." while singular was marked wrong "the bagpipe is a windbag instrument". .
English is a bit weird when it comes to bagpipes: Even when referring to a single instrument, you commonly used the plural form, "bagpipes" (presumably because each instrument normally has multiple pipes; a chanter and one or several drones).
Klingon doesn't do this: DIron is grammatically singular when referring to a single instrument.
That being said, I can see how this can be somewhat confusing. Since it appears that saying "a bagpipe" is grammatically correct (although perhaps slightly less common), I've changed the primary translation to "A bagpipe is a windbag instrument.", although "Bagpipes are a windbag instrument." is also accepted.
I don't think I have ever heard "a bagpipe" used in English. However, per Merriam-Webster, that is an acceptable usage:
I would keep the old translation as the primary one. Most people say bagpipes, not bagpipe. Sometimes Klingon and English use plurals differently, and I've always thought using this word and some others like it was a good way to teach that.
As you see, I know very little about bagpipes. Now I know that a bagpipe is really bagpipes. Thanks!