I am not exactly sure I believe the claim, but according to this report astrobiologists are now seriously looking for Earth-like moons orbiting the hundreds of extrasolar planets known so far.
The trouble with those extrasolar planets is that, due to the limitations of the methods of spotting them, all that have been found are closer to Jupiter than to Earth in size, so non-habitable if only because of the crushing gravity. So it makes sense to look for Earth-sized moons orbiting those gas giants. Except that you're looking for an ultratiny wobble in the orbit of the planet, which itself is only detectable as a tiny wobble in the position of the star or as an even tinier partial occultation. My gut feeling would be that this second degree wobble would be so deep in the noise as to be undetectable. But good luck to them, anyway.