If an area of the CPU heatsink wasn’t being cooled very effectively, the temperature in that area might not be reflected in the original design’s exhaust temperature.
Furthermore, there are reasons to suspect that Sony’s changes improved the cooler rather than harming its cooling ability.
All else being equal, we would expect the PS5 with the higher exhaust temperature to also have a hotter heatsink and a toastier CPU.
The fact that the new console is exhausting hotter air is not enough to establish whether the actual CPU is running hotter.