

The guideline (as applied) contains a contradiction, so the principle of explosion applies.
Specifically, there is a contradiction between “native-sounding English” and “no grammatical errors”, when the latter phrase is interpreted in the manner seen here. Native speakers quite often use sentence fragments and in other ways do not follow schoolbook “proper grammar”. In fact, second-language learners often use schoolbook grammar where a native speaker would use a more relaxed register.
Since the guideline contains a contradiction, it is either impossible to follow (i.e. forbids all communication whatsoever) or impossible to violate (i.e. forbids no communication).
Okay, let’s skip the formal logic talk then and go straight to linguistics.
The question “Good to merge?” does not contain a grammatical error. It is perfectly well-formed by the grammar that native English speakers actually follow in everyday communication. A grammar that fails to parse “Good to merge?” in context cannot parse native English speakers’ actual output.
Schoolbook English is not native English, because it’s not how native English speakers actually speak. Schoolbook English contains rules that directly contradict native English speakers’ everyday usage.
(Standard examples include the rule against split infinitives and the rule against ending a sentence with a preposition. These are not grammatical rules of English as it is spoken by native speakers. To boldly assert them is silliness up with which I will not put.)