Although we disagreed in the last thread about the order of operations, in this case I agree with you, because this is a riddle. It's not a straightforward thing, and that's what I mentioned from the beginning.

I have a feeling that the "composer" of this puzzle intended it the way Handy figured it out, but you and I both had logical reasons for what we had as well (which is why I said from the beginning I was not adamant about my being right --- I perceived there were other ways to look at it).

So, why are there (at least) 3 solutions to this problem? Simply because there are not enough points to create a true pattern.

It's like giving two points (x,y) on a a plane and saying, "state an equation that uses these two points." The simplest would be a line, but one can use them for a circle, and ellipse, a parabola, etc. So, more information has to be given if the answer is something specific.

This is why on IQ tests that sequences often have more than 2 terms, maybe 4 or 5--- because one can possibly find more than one pattern with only two terms.