That is definitely how your web browser accepts requests from other applications. Normal drag n' drop (into a running app) may not work that way (it does not in GTK) but in the case of starting the app fresh, you're probably right.
edit: Incidentally, BEN10 - the effect of command-line arguments can still be seen in a GUI shell - when you drag a file and drop it on an executable, that executable is automatically started and the file is opened. Try it with a text file and a shortcut to notepad. Or with Microsoft Word. That's probably done through command line arguments in the background.