I think this is very much an "eye of the beholder" question.
Ski descents of highly technical mountains often require rappels or down-climbing at some point. To me, if somebody had the cojones to stitch together a line consisting of ski turns down snowfields connected by rappelling or climbing in places where there's no snow, then I'd personally call that a "ski descent".
Style points count for something, which is why there may be many "first" descents of a given peak as people ski more and more difficult specific lines. For awhile, there were even sub-categories to cover first descents by alpine skiers, tele skiers, and snowboarders (with even finer sub-categories to separate descents by men or women).
In my book, if someone successfully hauls a pair of skis to the summit of K2, almost ANY ski turns they make would count as a ski descent.