"A Klingon does not defect."
In English, the indefinite article in "A Klingon does not defect" seems to imply that we're talking about Klingons as a whole, that it would be unthinkable for any one to defect, equivalent to the sentence "Klingons do not defect". However, as far as Klingon (the language) is concerned, this sentence is equivalent to "The Klingon does not defect." Obviously context matters, but would it be possible for the translation given here to have the same connotations as the English sentence?
You are correct: the Klingon sentence is not as narrow in meaning as the given English sentence.
cheHbe' tlhIngan could mean:
A Klingon does not defect
The Klingon does not defect
Klingons do not defect
When you say the Klingon sentence, you're not just saying one of these, you're saying all of them at once. Only context can narrow the meaning.