Because X over SSH requires a somewhat low latency and high bandwidth. The guy's requirement is unpredictable latency and low bandwidth (like 3 kbps). X is no fun at all over that kind of connection.

I find X-over-ssh unusable over anything non-local, even over local wifi it stumbles: the latency is especially painful. There's Xpra, which makes this somewhat bearable even on mid-level residential connections (unimpressive speed, high latency, horrible jitter), but for single kB speed, even plain ssh is really bad (with mosh making it just bad). This would make the result not-quite-horrible.