"Allopathy" was a term coined by Samuel Hahnemann in, I believe, the early 1900s to describe the practices of "orthodox" medicine. This neither alluded to nor meant that an "allopath" held a certain medical degree, such as an M.D., and this did not mean that allopaths in the early 1900s necessarily used treatments which produced symptoms opposite of those caused by disease -- this interpretation you found is inaccurate.
Hahnemann coined the term "allopathy" because he was a practitioner of "homeopathy," and in fact, I believe Hahnemann is considered the father of homeopathic practice. "Homeopaths" apparent practiced, and still today practice, in the belief that prescribing treatments that mimic the symptoms of disease leads to eventual cure. I have not read much about homeopathy, but understand that this is the root theory of the practice.
Now while allopaths did not necessarily hold an M.D., most of those described as "allopaths" were in fact Doctors of Medicine (M.D.). There were M.D.s of the early 1900s before the birth of scientific medicine who practiced "magnetic healing," "hydrotherapy," and other un-orthodox forms of medical practice.
Today the term "allopathic" refers exclusively to physicians who hold the M.D. degree, and is a term that has pervaded just about every level of American society. US Government websites often refer to M.D.s as "allopathic physicians," as opposed to "osteopathic physicians," which refers exclusively to those holding the D.O. (Doctor of Osteopathy) degree.