Is it not the usual supposition that multi-cellular life evolved because it improves the facility of individual genes to achieve maximum self-replication? The suggestion then is that, given enough time, the lab based yeast might have achieved this in any case, it just might have taken a few million years longer than the scientists had. Introducing an artificial environmental pressure just jockeyed the process along a bit. The point of the exercise, perhaps, was not to explain exactly how multi-cellular life actually first evolved, but just to highlight the fundamental possibility for it to do so given the right circumstances, and perhaps to provide a small answer to those who like to claim that evolutionary theory is not falsifiable and thus not scientific.