There are two different forms of broken - something that doesn't conform to a published spec, and something that doesn't work on something with significant market share. The person you're replying to is referring to the latter.

It's a colloquialism referring to a users broken expectations. If a user tries to open a page and it doesn't render properly, the user will blame the page, not the device. If a website renders wrong, that's the websites problem.

If the site uses a feature that is unsupported (or poorly supported) by a browser with significant market share, then its the sites responsibility to fail gracefully. You can rant until you're blue in the face about how the iPad/Safari should handle these things better, but most users simply don't care about your particular definition of "broken". They only know the site doesn't work.