Whenever I hear people talk about disordered eating, I remember those years of being, on paper, an alcoholic. The best way I can think of differentiating between an eating disorder and disordered eating is to remember why I was always so certain that I wasn't an alcoholic.
I think eating disorders, like alcoholism, are all encompassing. You don't get to choose to have a day off because you're a bit skint or you don't feel much like it. You don't pick to turn off your compulsions because you're on holiday or don't want to upset people. You don't get to just make a decision to stop obsessing because it don't fit in with your lifestyle any more.
I think disordered eating is a bit less intense. You might get to choose to have a day off because you can't afford your poison or you don't feel 100%. You might get to pick to turn off your compulsions because you're away or you know that acting on them would upset people around you. You might even get to make a decisions to stop obsessing because it doesn't fit the way you live any more.
Sometimes, I think people opt to say that they have disordered eating rather than an eating disorder because they're afraid of being judged. It probably gets around some of the awful 'you don't LOOK like you have an eating disorder!' type comments that everyone feels like they have the right to make. Or maybe they're not ready to accept that they do have an eating disorder. But, then, there are people who genuinely do have disordered eating- hell, I probably do, myself, these days- and are self aware, in the same ways I was during my drinking days.
It ebbs and flows, too. Like, I had an eating disorder and now I have disordered eating. It would be nice to say that my disordered eating will one days go completely, but I doubt it. I'll always be recovering. And anyway, by the same token, I may one day fall back down the rabbit hole to a full blown eating disorder again. In the same way recovering alcoholics generally need to stay away from alcohol, there are certain foods and things that I'll always need to avoid. I'll always have to be a bit careful, in the way I wouldn't have had to have been if I'd had disordered eating.
Really, though, I have no right whatsoever to decide what makes an eating disorder and what makes disordered eating. This is all just speculation and my own experiences. When it comes down to it, we're all the experts in ourselves and we should all be able to describe our eating however we wish.