I could believe these informations if Eurogamer didn't claimed the reported clocks are the one documented to devs. Those higher clocks are meant for the testing and I wouldn't be surprised if it was to test the stability of the device at higher clocks.
Late clock changes have happened in the past. Devs were originally told up to 2ghz for the CPU and 1TFLOP for the GPU (fp16 of course) so it isn't really outside their original target. Also it could be that chips were not happening in time for the winter launch and they ended up delaying it to spring because Zelda wasn't ready for Winter. That is my guess. If you don't have any software, you would have to delay the platform and the delay could have opened up the newer tech.
I can't not take this leak seriously though with him knowing all that he knew, it was legit info and him lying on clock speeds seem really weird, especially when they line up well with a node shrink in similar power consumption.