No it's not. It was the most sold during March, but that's it.
Local sources (https://www.autohome.com.cn/hangye/showroom/) tend to show that it's Xiaomi / Geely that's leading the race in 2026.
Additionally, sales numbers doesn't correlate with the brand image of Tesla : it is a luxury brand, no matter how you put it.
You're talking brands, I'm talking car models. And your own source lists the Model Y as the #2 best selling model cumulatively for 2026, behind only the Geely EX2 (星愿), which is a third of the price.
Also, you seem to be implying it's somehow a bad thing to have a luxury brand image with mass-market sales, but that's a pretty rare thing to pull off and it's also the key to huge margins. See also: Apple.
Look, Musk is a despicable human being, but the Model 3/Y has been a ginormous hit and it transformed the global EV market. Does he deserves all the credit for pulling this off? Of course not. But you need to stick your head pretty deep in the sand to pretend that a) it was not a success, and b) that Musk had nothing at all to do with it.
So you're technically correct, but IIUC Tesla is still the most delivered (customers taking delivery) EV brand in China. Draw what conclusions you will from that fun fact