Given how wildly the framework usage [1] differs from the long-standing and well known State of JS survey results [2], I'd be fairly wary of anything else they claim. Not saying the results are wrong, probably just different samples, more so that it seems the variance is way too high to get any useful insights.
This is a report for agencies. They cover a completely different set of customers and most of the time are called in to maintain. Maintaining leaves a little space to introduce new technologies and processes, which leaves you with older technologies.
Also, these companies have no reason to switch to other (newer/shinier) technologies since the software they deliver is tied closely with the chosen language. Switching would mean finding new customers.
State of JS is also biased to the group that opts to fill the State of JS survey. I do think it's a great survey with real value, but it's quite likely it's own distinct group too.
The survey in this article claims to have reached about 1000 times more people (though not all JS devs) than the stateofjs survey. I would expect some differences due to selection bias