As far as I know that's exactly right, it has to do with the possible sequential loss of systems 4, 1 and 2, due to common tubing on the brake lines.
Thus if you get HYD QTY LOW 1 without any problems on system 4 first, your problem is with system 1 only. If instead you get a HYD QTY LOW 4 followed by HYD QTY LOW 1, you may well be in the multiple sequential loss scenario; the checklist then directs you to depressurize system 1 (to conserve fluid) until required for gear and flap extension.
MD