How is having the option, besides Windows, to order the laptop preinstalled with a default, well tuned and well supported Linux distro a "walled garden"? Also, most patches in this distro would presumably end up merged upstream anyway.
I was referring to the prospect of their spending time working on their own distro, at the expense (considering the finitude of human lifespans etc) of supporting others. As with so many arguments, your point makes total sense until you consider that human effort is a finite resource.
And this is exactly why anyone who likes that approach can & will buy an Apple laptop. Framework is clearly going for the opposite of that market. Instead of being a (necessarily) worse clone of Apple, I think it makes sense for them to cater to the market they are clearly aimed at, which is not people who are happy with a walled-garden system.