It doesn't sound like the guy said, "Let us search for an external deadline so that we can rally this team!" Instead, it sounds like a reasonable amount of time

It doesn't sound like the guy said, "Let us search for an external deadline so that we can rally this team!" Instead, it sounds like a reasonable amount of time ahead he said, "Hey, there's a cool chance to demo this publicly coming up -- let's see if we can get it out there!" Sure, the guy was in some sense a manager, but this isn't some corporate situation with external motivation as one of the few rewards. It's a small team of people who are into the idea enough to work on it on the side, to begin with. The article presents this as an internally chosen external deadline, and those can often be really useful.