3393RP said:
No. Your knowledge of sentence structure is deficient. I did not say you were stupid.
I think I have to agree with Mooney Fan, that was a subtle attack on the person (perhaps not intended as such). Here is a definition
“stu·pid·i·ty
noun
behavior that shows a lack of good sense or judgment.
"I can't believe my own stupidity"
synonyms: lack of intelligence, unintelligence, foolishness, denseness, brainlessness, ignorance, mindlessness, dull-wittedness, dull-headedness, dullness, slow-wittedness, doltishness, slowness, vacancy; More
the quality of being stupid or unintelligent.”
So that only applies to behavior which is by definition performed by a person. Thus the original statement really meant that people who use that phraseology are engaging in a behavior that shows a lack of good judgement or sense.
And certainly stating that someone’s understanding of sentence structure is deficient is an attack on that person.