Not quite. The "no control" is (or rather, is not) over how the DLNA server serves the file.
As I point out later on, there is a specific way for the page to tell the browser that a link is meant to be downloaded as a file rather than opened, ie the "download" attribute of the link/anchor HTML element, which should be understood by recent-ish browsers. But
bad news, this isn't meant to work unless the link's origin (scheme+host+port) matches that of the page (though older Chrome-alikes might not know that), so it doesn't help with links to the DLNA server, and, as the documentation explains, some browsers might believe the HTTP headers instead, or just not know about it (IE).
Thus the only real solution is for the WebIf to proxy the DLNA server so that the file is served with headers controlled by WebIf. I suppose
there must be a way to do that within the Jim/CGI/lighttpd framework, if it were sufficiently important.
As was researched earlier in the thread, current browsers have forgotten how to pass streams to helper applications, so essentially rendering and downloading are the same, except that in the former case the downloaded file may be transient and its location hidden from the user. This is why the new Play button has to fake up a playlist for "downloading".