First, you are assuming that the person is providing incorrect/misleading information. Second, you are assuming that the reason is because the person has no chemistry training. Third you are assuming that I would ask for qualifications.
Training in a particular field does not ensure competence. There are many chemists, doctors, engineers, plumbers, musicians, lawyers, etc who are incompetent. Conversely, there are many self-taught people who are highly competent in a given field. I judge an analysis, a review, an opinion, an essay on the basis of its content and its merits or flaws, not on the basis of the qualifications of the person who wrote them. Why do we have peer review? If all it takes is qualifications, then all contributions to a journal by a qualified individual would be accepted automatically.
Your original statement was "The usual arrant nonsense by a non-musician critic." Basically, you are saying that non-musicians are usually incapable of providing a sound criticism, review, or opinion. Conversely, there is a (strong suggestion, I think from reading what you wrote here and in other venues) implication that, almost exclusively, musician critics have such capability. If we were to extrapolate your statement to other fields, then we would have to disregard book reviews written by non-authors, analyses of paintings by non-painters, reviews of films by non-film makers, etc, etc.
I will agree that there are some technical features in all fields of endeavor that require some specialized knowledge. Of course, it all depends on the depth of the essay or analysis in question. Some comments are general, others are very detailed. But I do not agree that only practicing people in that field have a monopoly on the knowledge that is necessary to provide a sound piece of criticism or analysis.