The authors had previous knowledge of chef. But the aim is not exactly the same. I have used the three, and the fact that pallet is essentially a library helps factor your infrastructure in your application, and thus goes beyond the ability that chef and puppet provides. This become evident when having to express inter-dependencies between spread out pieces of your infrastructure.

Currently this comes with the price of a steeper learning curve, but the benefit is well worth it, as far as I'm concerned.