Per your screenshot, the headers/responses indicate that your browser loaded a cached version of the script file.
The 'cache-control' in the response is set to '0' which, effectively, means that the browser should check the last-modified date and only load the file from the browser cache if the cached file is the same age or newer. (If 'cache-control' was set to 'no-cache', then it would mean the server was telling the browser to never load from cache, i.e. always load from the server.)
The '304' response confirms this - it means the browser followed the server's instructions. The browser compared last-modified dates, finding that the file on the server doesn't have a newer modified date, so it just loaded the file from its cache.
HTTP headers, including 'cache-control', are not a simple concept to understand. If you'd like to better understand, you might try reading through the spec, or doing a search to find some of the more human-readable explanations out there.
Here is an article that talks about embed code (how to add them) http://adobe.ly/1fD4Gm7 . You may refer to this article as a start. Please let us know if you need additional support. Would be glad to assist.