You don't know how productive those developers were on those projects, nor do you know if TS would have made those developers more productive. Granted, the original claim wasn't comparative, but that's the point I'll make anyway.
Interesting theory, let's see how it plays out in the marketplace. If typed languages are indeed more productive we should see them start to win out in, say NPM, right? Today the overwhelming majority of NPM modules are JavaScript, but if the same modules can be written more productively in TypeScript or Dart or another typed alternative, you should start to see those modules win out. Fewer bugs, more able to concentrate on features.
Indeed over the long term modules isn't a bad idea as the interface requirements and discoverability would benefit massively from better tooling, a la optional typing.