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.