It's really not a hard concept to wrap your head around.
Original Kinnikuman Kinkeshi were made and sold in Japan. They are made from a soft, eraser-like material, and there are 418 sculpts in the original run.
In 1985, Bandai sold the rights to distribute the toyline to Mattel. They chose about half of the figures from the original toyline, and using the same molds, cast them in a harder rubber material. They were sold in North America as M.U.S.C.L.E.
So, to answer your last question, the American toyline consists of the figures that were sold in North America, even though they were manufactured in Japan.
The Japanese toyline refers to the softer figures that 1) came out first, and 2) were sold in Japan.
The poster we refer to was also only distributed by Mattel in North America, and only has figures that were released in North America featured on it. There are a handful of figures that were made in the same, firm M.U.S.C.L.E. material that do not appear on the poster, such as SHA, BHS, the Mag 11, etc. Those are the Non-Poster figures, i.e. they are made from American M.U.S.C.L.E. material but not featured on the American M.U.S.C.L.E. poster.
Remember, they have to be M.U.S.C.L.E. figures not featured on the M.U.S.C.L.E. poster to be considered Non-Poster Figures.
A Kinkeshi is not the same as a M.U.S.C.L.E., therefore it is not a Non-Poster figure regardless of what the sculpt is.
M.U.S.C.L.E. is the American version of Kinkeshi, made in the same factory but of a different material from the Japanese originals.
Even though M.U.S.C.L.E. figures are exact copies of Kinkeshi, not every Kinkeshi was made into a M.U.S.C.L.E. figure.
Also, there are a few M.U.S.C.L.E. figures that are not featured on the poster, even though they are made from the same material. Those are Non-Poster Figures.
On a side note directed to the choir, after seeing someone struggle with such a simple concept, is anyone surprised at some of the ridiculous auctions you have seen over the years? Although I cannot deny that greed plays a part in bullshit auctions, I feel that poor reading comprehension skills are a far greater contributor to such situations.