I'm not entirely sure what's meant by that comment. The form factor appears to be sticky, so the first time you just click the desktop icon instead of the mobile icon and it will always open in desktop mode.

That said, don't assume your users aren't using mobile browsers :) Based on the videos, that's the intention behind the change. A non-sticky setting would be annoying, but putting it front and center (rather than buried under emulation settings) and having it selected the first time you open dev tools will hopefully get more web site developers thinking about this stuff earlier in the development process.