Yeah, but to take the fact that there are other leftist candidates in play to say that the "left" isn't running a primary is equivalent to saying the "right" didn't run a primary because Le Pen is also running.
Anyway, that's splitting hairs. Macron's strategy is to point out that Fillon is nearly as much a danger to the values of French liberalism as Le Pen, and also that he's a bit of a shit candidate. Would try to turn the runoff into a referendum on Le Pen then. Amazing really that it looks very plausible that neither of the big traditional parties of left and right might make the runoff.