Not necessarily. I'm going out on a limb and guessing at what they're using under the hood and if I'm right then font rendering wouldn't be the issue. I assume it's some sort of app that uses webkit to render pages then x-server to create the png. So in my experience, what's usually the problem for me is my own markup. If you're not meticulous about cross-browser consistency then this sort of stuff happens. It's not that it looks terrible, but it's just disappointing as it's not what you're used to seeing or what you want people to see.
I can't guess at exactly what they're doing, but when I built something very similar we noticed bad font rendering across the board until we tweaked the font rendering. It's often as simple as choosing a better font to use as the default when one is not specified.
