They make it very clear that they are praising
small commits, and squash merge commits are
usually not small. Squashing is the opposite of what they want.
The preference they have is not exactly a problem with github PRs, but github PRs are much more likely to review a big pile of code at once.
The amount of code being reviewed at once is a meaningful and extremely objective measure, and that's the thing they're concerned with. Not who made it.
