Countif on filtered data - how does it work?

I needed to apply countif on filtered data. As always, a quick google search and I found the solution:
=SUMPRODUCT(SUBTOTAL(3,OFFSET(Y9:Y202,ROW(Y9:Y202)-ROW(Y9),0,1)),--(Y9:Y202="X"))

Now, I have a very basic understanding of SUMPRODUCT, SUBTOTAL and even OFFSET, but there is one thing that I can't understand. The "ROW(Y9:202)-ROW(Y9)" should return 0. Obviously it doesn't, since the OFFSET function wouldn't work with that, but I don't understand why? What am I missing here?

Thanks a lot..