Alot of people seem to think Google only crawls content found via ANCHOR elements, but for a long time they've been able to extract the path from EMBED, SRC, and other markup elements that indicate a remote resource is being included; but that's a far cry from being able to process and execute scripting languages and understand the DOM transformations happening from AJAX requests.

In your case, I'd suspect they were simply following the src of your: <script src="path here"></script> markup... though if you read the articles cited, we suspect they've been crawling and understanding JavaScript for a pretty long time now.