They mean the fact that the game came out in instalments, which is a ridiculous complaint and has nothing to do with the topic at hand.
Considering that each installment might as well been a different game, just using the same engine and graphics, I agree that it is a ridiculous complaint. Each installment had a 12hr+ single player campaign + 12hr+ co-op campaign + completely different multiplayer experience.
However, Starcraft 2 is complete and been this way since the inception. They added microtransactions years after the full release, and they all boil down to cosmetics and other completely optional and non-necessary things, like skins and banners, i.e. cosmetics. Something for hardcore fans to buy in order to support their game, but absolutely non-essential for the actual full experience. And I am saying that as someone who hasn't spent a single dime on Starcraft 2, aside from buying the full game on release (+the expansions that came out years later) and putting hundreds of hours into it.