If constructive criticism was your intent, it would have been constructive to make that intent explicit. Especially in written communication, if one wants to p

If constructive criticism was your intent, it would have been constructive to make that intent explicit. Especially in written communication, if one wants to provide constructive criticism (as opposed to criticism which is indifferent or just being critical to be critical), then it is important to signal that somehow. Possibly with words ;) Of course not signaling that doesn't preclude the receiver of said criticism from using your critique constructively, but, imho, considering the minimal time needed to say something like "This is intended to be constructive criticism," and that doing so is not some sort of "happy-good-energy-no problems" use of language at all (your critique can still be as vigorous as desired), imho, there is no good reason not to and many good reasons (never knowing where the other person on the internet is coming from, improving one's own communication skills, increased explicitness, etc) to do so.