The conclusion is very probably correct, but the study in no way proves it.
First, the numbers are too small. They are not large enough to eliminate the possibility of random genetic drift.
Second, the study does not seem to look at any genetic change at all. So where is the evolution?
The change in time of first birth is well within the normal human range, and is very moderate. The change in age at first birth could easily be explained by a very slight cultural change. If stuck on an island, where choices are limited, what is to stop people from getting married earlier, and starting families? Presumably everyone has a job lined up, so there is no wandering around deciding on a career, or pioneering in a new region.
Possibly the greatest measurable amount of human evolution to occur in the 20th century was WWII, particularly in the European Jewish population where half were killed. Which Jews tended to survive and what genetic impact did it have? The Jews alive today, the descendants of the holocaust survivors, likely score higher in many areas than the Jewish population average before. Tribal warfare is the special evolutionary pressure that drives human evolution, and has been for a very long time. For the last several thousand years Jews have particularly been on the receiving end of it, the victims of leftist envy.
One large amount of de-evolution occurring right now is with smart women. The smarter the woman, on average the fewer children she will likely have. The result is a growing gender gap. Women will become increasingly less intelligent than men. The political gender gap will also increase. Women will increasingly becoming socialists and support higher taxes on the producers, and men will increasingly become conservatives, against higher taxes and increased regulation by the socialist non-producers.