Works for me.
?
Because its cached for you, since you saw it already.
What is this magic. But wait, when I post images onto this site, I just copy and paste. Why does that seem to work?
The basics:
When you go to a web page, you tell the site's server "give me this document." That document is the html for the page. From there, your browser parses the html. It uses what it finds to figure out what else it needs. Those other things may be on the server, or they may be on another server. When asking for those other things, it tells the server it is asking where the resource was originally being called from,
as per this specification. Usually, a server doesn't care, and just serves the information back, be it images, videos, CSS or scripts.
So, if you they copy the image URL directly, then post the image elsewhere, you are saying "Server A has the web page being accessed. Server B has the image being accessed." That's hotlinking. So you then have someone access the web page on Server A. Their browser then looks at the page, and figures out it needs the image on Server B. Well, in some cases, Server B doesn't like when people use their bandwidth for running someone else's site's images. And so instead of ignoring the referrer, it looks at the referrer, says "this isn't me or anyone I host images for" and so returns incorrect content; an image telling you not to hotlink.
The cache is also something which comes into play. If you visit Server B's website, on which the correct image was stored, that image is downloaded and stored in your browser's cache. When you then go to Server A's website, it skips the step of asking Server B for the image, and instead uses the cached version; saving both time and bandwidth. So as a result, the original hotlinker sees the original image, while anyone else sees the anti-hotlinking message.