What the author encourages is that the designers work more free-flowing with sketches and wireframes and that the developers take over earlier to bring that into a workable structure. And that the collaboration between designer and developer doesn't stop at an async hand-off, but that they finalize the design together -- in code.
Some of the commenters here seem to be annoyed at designers that make "hard to implement designs" and therefore think they want designers to constrain everything with auto layout. But this doesn't address the cause of the issue, which is designs being made by designers in isolation, which are then being treated as gospel for developers to 100% match. This is the real problem.
In my opinion the gravest issue with Figma encouraging this workflow is actually the feature gap. Figmas feature set is extremely underpowered in comparison to CSS. Figma doesn't even have grids. If designers are now building stuff only with the tools that Figma allows, all the cool and creative ideas that developers could bring in, because they are actually pretty easy to implement on their platform (the designer just doesn't know about it) will go away.
I can only recommend you this talk by Matthias Ott: https://www.youtube.com/watch?v=1Pq7VqNrtk4