Rediscovery of "extinct" species is common place, because of the inherent difficulty in proving that all individuals of a given species are dead. Combine this with the robustness of biology, allowing species to quickly boom under favorable conditions, and then false extinction ends up happening more often than you would probably suspect. It's normal for many healthy populations to fluctuate wildly around a given carrying capacity. r-selected organisms are particularly notorious for having like 95% of the population die off regularly, and then bouncing back in a few years.
In the case of the thylacine, it's a macro organism so it probably has a higher profile when compared to a small gecko. So the likelihood that they're still extant probably isn't quite as high, unfortunately.