Can an article include "A Comparative Study" in its title if its main purpose is not comparison? If the main purpose of an article is to present/introduce a new method, can it still be entitled "A Comparative Study"? Or does it depend on how much of the article is devoted to the comparison of related methods? I am asking from the perspective of a reviewer.
In many ways, the title of a scientific work can be thought of as a super-short abstract. In other words, it should tersely summarize what a reader is likely to find most salient in that work.

Thus, if you are a reviewer encountering a title that you find misleading as relates to the content, then it is entirely reasonable and appropriate to suggest that the title be changed.  As flaws in a paper go, however, I would find it pretty minor from a reviewing standpoint, since it doesn't much affect the content and is very easy to fix.