Comment by MatmaRex

You're right, but the author's approach still works by accident, because ClearType is disabled when drawing text to canvas. I am not sure why that's the case, but I would guess it's because the subpixel colors can only be computed correctly when the background color is known (and static), and with a canvas, the background can be drawn later or animated. ClearType is only enabled for normal text on the page, and many CSS properties incidentally disable it presumably for similar reasons (e.g. 'will-change: opacity;').