It's not wise for me to continue the discussion if you are going to resort to mudslinging. I can not simply explain something at the sandpit level, especially not to someone in an highly emotional state.
[this part contains sarcasm]
If you read between the lines in the article, and I've read it in other Facebook articles too (between the lines), understanding code is a problem for Facebook, it's against their principle of "go fast and break things". Good that they are not into the self driving cars business :P
[/this part contains sarcasm]
Traditional web development is a bit different from traditional development with long compile times. In PHP for example, the code is evaluated on the go, for every request. Development goes like this: Make change in .php file, (upload the file), reload the browser to see what happened. If you add a type-checker between, before they see what happened, it will slow down the development process. This is how static types and type checking slows down development by adding a compilation step.
Facebook claim they fixed it, but it's still a concern that need to be addressed when adding static types to other interpreted languages.
I do acknowledge that tooling allows you to see type errors directly in the editor/IDE before you reload the browser.
You can however get that without static typing, via inference. (type annotation do make building such tool easier).
It's however likely that the bug would be discovered during the manual or automatic testing anyway, so you have to evaluate if the added complexity to dev-ops from changing the language to add static typing, and adding a compilation step, is actually worth it.