I guess it isn't, and it seems to me it should be.  But I'm not a researcher, and I leave it to the research community to figure out if this is an interesting metric for them.  I can tell you it's an interesting metric to _me_, because making 1 edit some time within six months of registration is _much_ less meaningful than making at least 5 edits a month (which is the active editor definition).

(I note that https://meta.wikimedia.org/wiki/Research:Active_editor is not in the above category, and is also not defined on Meta.  Once again, I'm not taking it upon myself to fix those pages, as I feel they are !owned by others.  But it behooves us to get these a little more aligned.  CCing Dario and crossing my fingers.