^^
OK, here’s what is happening on my paper and it might explain the different counts on steps. I realize I did collapse steps as I wrote down the two equations (to help the subtracting) as follows:
3x =5 - 5y
2x =7 - 3y
I admit that I did evaluate the given equations and was looking for a way to isolate a 1x on the left side and “hopefully” find a (y+1) on the other side. What I did get is x = -2 +2y
My next lines could have been x = -2(y+1) or -1/2x = -1/2 (-2+2y)
My “one” step solution stems from making those manipulations in my head (as I see them) but I understand that one considers those as additional steps. Anyhow, why I considered the -1/2 as the only answer is because from looking at the line above, I knew that the (y+1)/x has to have a negative solution. I did not consider the -11 as a viable solution and I eliminated the two positive answers. On this note, I think that something can be learned from the “arcane” methods used by good test writers. Although I cannot demonstrate this with great effectiveness, I think that one could see a “hint” in the proposed answers that points to 2 and -1/2 being the “plausible answers” as they are somehow opposites and could yield to both the correct answer for the astute and the erroneous one for the careless student. I find this behavior common on the SAT – well the older versions that is.
For all intents and purposes, were I to have to explain to a student how to approach this problem, it would be a better idea to follow the methods described above, and not try to explain my “intuitive” or “visual” methods that rely on the type of equation balancing my Eurodad taught me. His words were “switch sides and change the sign.” You need to add the accent for full effect. 
Not sure any of this is really helpful, but I tried to explain how my mind works! One thing, however, that I think is essential in the problem is to keep the focus on the “solution” that includes the full term (y+1)/x as opposed to solve for both x and y.