as was said above the term "current source" and "current sink" are relative terms. going purely on the physics, you could probably state that the circuit that uses an NPN is a current source and the circuit using a PNP is a current sink, because the first is a source of electrons, and the second is a "sink" of electrons. but looking at it that way in modern electronics can be confusing when analyzing a circuit. for instance, current sources and their "cousins" current mirrors, are used in amplifier designs, and only their function is important, not their polarity. an amplifier using NPN transistors for the diff amp, will have an NPN current source, and the following voltage amp stage (a PNP) will have an NPN current source as a load. the same input section can be made with PNP input devices, current sources and NPN voltage amplifier. the functions are identical but the polarity is reversed. they are still called current sources because their function in the circuit is the same. if you want to get really technical, the voltage amplifier load is a current sink, because it's a load, but it will still be called a current source. the terms are somewhat interchangeable. i worked with someone who had worked on tube amps most of his career, and had a really difficult time getting his head wrapped around the concept of current sources being either polarity, and really had a hard time understanding current mirrors. i'll be adding a "quickie" cash course in basic amplifier theory to my blog if it will help clarify this.