No, an abrasion (in the medical sense) does not have to come from abrading the skin. Just like the medical use of the word chronic is misunderstood, Dr. Meyers use of
abrasion misleads laypersons to misinterpret parts of the AR. He also called the red mark on her neck and the large spot on her cheek abrasions, but he doesnt attribute the cause in either case. An
abrasion, despite its etymology, is simply a term for a relatively low degree of damage to the outer surface of skin regardless of its cause.
From Wikipedia:
We all think of an abrasion as something caused by a rubbing action which causes some type of visible damage to skin. But when a forensic pathologist sees some type of damage to the surface of the skin and doesnt know the cause, he refers to the area as an abrasion because of its definition in dermatology. In other words, he is not addressing its cause, but rather its appearance. When we think of a cut, a bruise, or an abrasion, we think subjectively to the cause of each. When a pathologist uses these terms, he/she is thinking objectively toward the appearance only until he/she establishes the cause.
The abrasions Meyer noted on her back could very well be from her being poked by some object such as has been theorized by Kolar.
The "difference of 2/16 inch" (1/8") is the difference between the largest and smallest approximations taken from two different marks:
(BTW, MEs usually use Metric measurements as shown on the the American Board of Forensic Odontology (ABFO) forensic scale in the photo. I don't know why Meyer used Imperial measurements here instead of Metric, which would be much more accurate.)