implies that any usage of ethics in opposition to the study of Aristotle's eudaimonia was at one time as irrelevant/improper as the common usage is now.

Uh... ethics is the study of the good. Aristotle has arguments which conclude that eudaimonia is the highest good. But that doesn't preclude other investigations into the good life. In any case, I have no problem at all with introducing new questions or inventing distinctions. I have a problem with amateurs working in a field and altering the usage of professionals for no good reason. It is bad form and reflects poorly on us. I really doubt that we need to change our definition of the word ethics to be capable of understanding the distinction you are trying to make.

I think, while that statement might be correct for a technical field's vocabulary, it is not alright to restrict a layman's usage of certain philosophical terms, like ethics, in the same manner.

A layman can use whatever words he or she likes. But if you want to study a field use the terms as others in that field use them, unless there is actually a problem with that terminology.