Which models did you look at? I don't remember a lot of models that are new to the market recently. I checked the Mazda CX-3 and the Nissan Leaf, and the Model 3 does appear to have crushed both of those based on first year numbers.
It would be possible to argue that Tesla outproduced the Mini Cooper (depending on how exactly you shade the first year of production).
The others handily beat them, with the 1965 Mustang crushing Tesla...
(It's a genuine question. Yes, the Mustang was based in part on the prior Falcon platform. Wouldn't Tesla sensibly base the 3 in part on the S in the same way Ford continued to sell the Falcon alongside the Mustang? If Tesla is sharing literally nothing across models, that seems like a non-sensical way to run a car company to me.)
Still it's the pro-Tesla person that's making the claim; the onus is on them to provide the numbers or if it's not a fair comparison, to avoid it (or clarify it).
That's why I asked what models the other person looked at because so far all of the information I can see from the site that they linked confirms the "pro-Tesla" person's statements.
Chevy sold over 200K Corvairs each of the three first years of launch.
First 12 months deliveries of Tesla Model 3 were a little over 26K. First 15 months deliveries (which is more apples-to-apples with other company "first year" launches) were a little over 80K.
It's not even close, IMO... Do you see the figures differently?
Tesla has been limited by production of batteries and cars, now they have scaled those a lot. But they aren't the fastest of history, that seems clear. Unless they suddenly sell 125k cars a quarter they won't catch Mustang.