Calling a sentence ungrammatical is a statement of fact -- or wrong. Something is in the passive voice, or it isn't; something is a run-on, or it isn't; something is a sentence fragment, or it isn't. It doesn't mean that you don't like the sentence.
You can write without knowing all the grammatical terms. You can even crit without knowing all the grammatical terms. But if you do crit without knowing them cold, don't use them. Nothing undermines your credibility more than saying a sentence that, if diagrammed could be used for a coat-rack, is a run-on, except perhaps saying "Nothing happened" is in the passive voice, or saying that a compound word has to be two words, even when it's a location's proper name.
The irony is that the people who do this miss that you can criticize a long, convoluted sentence as long and convoluted, without calling it run-on. And grammatical errors tend to slide past the eye unless there is something else wrong with the sentence. If you're not sure that some sentences are really fragments, you can still complain that it's choppy. Etc.
Then, on the other hand, ungrammatical structures have their uses. Run-on sentences and sentence fragments can be useful for stream-of-consciousness, for instance. So there really are no rules, no absolutes for the writer. But when you are critting, you are not writing your own works. You can quibble about whether this particular violation is any good, but whether it is actually a violation is not a matter of opinion.