I think you've misunderstood his question (although interestingly enough, I've also done research on pseudohyphal growth in yeast).
weirdboy, the article is a bit misleading when it says that yeast were once multicellular, albeit in a way that popular science reporting very often is. What it means it that the ancestors of yeast (which probably weren't especially yeast-like) were multicellular organisms, and the that yeast unicellularity is a fairly new trait (on an evolutionary scale). This sort of "reversion" (from our multicellular biased point of view) happens pretty often in nature.
The critics are entirely right, in my opinion: while this is an interesting study, it probably has almost nothing to do with the original evolution of multicellularity. As Brewitt says, the biochemical pathways controlling hyphal growth are largely still present in yeast -- they're just "turned off".