+90% users in the past 3.5 years
huh? That is incredible growth. How is it even measured?

Herb's blog post links to the SlashData Developer Nation Survey, so presumably that's what the claim is based on. The company has a methodology page here [1], and it looks like the Developer Nation panel [2] is one of the sources used by that company.

[0]: https://www.slashdata.co/research/developer-population

[1]: https://www.slashdata.co/company/methodology

[2]: https://developernation.net/

Has anyone heard of any of these companies before?

And I wonder what the number is for other languages.

They want my email just to look at their "free report". Sorry that's not good to happen.

You can hear the engineer in that second question. They hear a wild statistic pulled out of someone's ass and ask what is that sticking to the side?