What argument? What the article says is:
1. Evidence doesn't support the idea that static types reduce bug density.
2. Static types are cool anyway because they enable useful developer tools.
3. If you want to reduce bug density, lots of evidence supports the use of TDD.
How does:
I’m not aware of any empirical evidence that static types have a strong impact on bug density.
lead you to make the assertion:
So in spite of the cool developer tooling they enable, **static types don’t actually help reduce over-all bug density by very much.** [emphasis in the original]
especially when the only real study you quote ends with "we are unable to quantify the specific effects of language type on usage"