What the ghosting test shows
Ghosting is a trail left behind a moving object because the liquid crystal cannot change state fast enough. It is most visible on a dark background with a bright object, at moderate speeds — very fast motion is hard to follow at all, and slow motion gives the pixels time to keep up.
This page draws no motion blur whatsoever. Every block is a hard rectangle on every frame, so anything smeared behind it is the display, not the picture.
How to see ghosting
Track a block with your eyes as it crosses the screen, then try again looking at a fixed point and letting it pass. The two produce different results, and the second is closer to what a camera would record.
If your monitor has an overdrive or response-time setting, change it and run this again. Too little overdrive leaves a dark trail; too much causes overshoot — a bright halo ahead of or behind the object, which is usually worse than the ghosting it was meant to fix.
What this test cannot tell you
A browser cannot measure response time. It cannot see what your pixels did, and it does not know when the panel actually finished changing. What this gives you is a clean moving reference so your own eyes can judge — which is the same method every reviewer uses before reaching for a photodiode.