WHAT devices that are similar to "that" size "generate" power?
Piezoelectric elements are common and can be made in a pretty arbitrary size, most are actually smaller than that device. I guess a regular moving-coil microphone could be made fairly small and would generate power. I've seen some pretty small SMD photodiodes and I'm sure they'd be many other examples that generate power, albeit in tiny amounts.
Nothing in that article seems too pie in the sky to me, they are talking about a target of 100 microwatts afterall, not charging your iPhone while you go for a jog. Unlike a lot of other articles the target applications listed seem like fairly plausible applications for the technology.