The implication (at least my own) was not that Switch outselling PS3 in Japan is impressive in itself. It's simply a milestone on Switch's journey.
Switch outselling N64 globally wasn't an earth shattering achievement in itself, yet it was still noted as a milestone. There were articles and threads when PS4 outsold the 3DS even though a Playstation home console outselling a system that won't reach 80 million lifetime also wasn't exactly a mind-blowing occurrence.