Good point, the author clearly misses the point that tests themselves are code and thus can have errors in them as well. Code coverage is just a vanity metric if you're tests don't actually test the correct thing.

Types are also code and can have errors in them...

Types aren't code.

>I don't know about what the author's goals are, but I am in favor of offloading as much work to computer as possible.

The problem is that both writing more tests and statically typing your code involve extra code you need to write. Neither one comes for free.