Especially the part about TypeScript. My experience is that LLMs such as Claude Code work really well with vanilla JavaScript. Once you switch to TypeScript, you're tapping into a different language training set which is much smaller than the JS training set and which adheres to different conventions and principles.
The part about good test coverage makes sense though I don't know if 100% coverage is the specific goal to aim for. You can have 100% coverage in terms of lines of code but don't test the relevant parameters which cause issues.
My definition of good code is more about architecture; modularity, separation of concerns, minimal interfaces, choosing good abstractions and layering them appropriately, clearly separating trust boundaries with appropriate validation... Once the LLM sees certain things, it lets you tap into a "world class software engineer" training set.
A lot of the points mentioned in the article differentiate junior developer from mid-level developer... If you want the LLM to output 10x software engineer quality, the patterns are different and more nuanced... Goes beyond just having good test coverage.