No, they do mean possible moves and they don't mean maximum length game. There are on the order of 10^45 reachable chess positions. The article did not say that was the number of moves from one position. The article says 218 is the maximum number of moves from one reachable position--it's the whole point of the article!
Their post was edited to remove the part I was responding to; the "do" in my post was directly correcting the "don't" in their original post, and vice versa.
