Confusing article status for journals of American Mathematical Society: "reviewing" AND "being handled by an editor"
You should note that the word "editor" is used in many ways for quite different things. Most people understand it to mean "someone who makes changes/edits to the text". But that isn't how it is necessarily used. While the publishing industry does, in fact, employ people who do that, working with an author to improve the text, it usually means someone with some management responsibility. 

In the case of your paper, I suspect that a "managing editor" (a manager) has assigned your paper to a lower level "subject editor" (or some similar term) whose main responsibility is to track the progress of the paper through the system. He or she will find reviewers, track their progress, and collect reviews. When all reviews are in, that "editor" will make a recommendation to some higher level "editor" about whether to accept or not. If the overall decision is to accept, then your subject editor may assign someone to work with the author on improving the text - a traditional editor. 

I used the term "subject editor", not because it is a term of use, but because it describes someone who actually knows a bit about the subject of the paper and which reviewers would be good for getting advice. This is most likely the "editor" that the system is referring to. It means, roughly, "we are handling it and progress is being made". 

See the Scholarly Books... section of this wikipedia article for the typical usages. "Project editor" = "subject editor".