This study from the University of Reading found that severe turbulence has indeed increased significantly and measurably over the last 40 years: https://research.reading.ac.uk/research-blog/2023/06/28/avia...
But that's not what the paper says. It says Clear Air Turbulence (CAT) has gotten worse, not all types of turbulence. In this case, the flight flew through a convective storm.
Even so, the paper says there's been a 0.2-0.3% change in CAT:
> The largest increases in both absolute and relative MOG CAT were found over the North Atlantic and continental United States, with statistically significant absolute increases of 0.3% (26 hr) and 0.22% (19 hr), respectively, over the total reanalysis period.
> Climate models consistently project environmental changes that would support an increase in the frequency and intensity of severe thunderstorms that combine tornadoes, hail, and winds (high confidence), but there is low confidence in the details of the projected increase.
The models project it, but there is currently low confidence in the increase.