Read the actual paper and the story becomes far less exciting.
In brief, study participants were randomized to either lose weight quickly with an all-liquid meal replacement shake program (Optifast), or to lose weight slowly using that same Optifast shake to replace one to two meals daily. Once a target weight loss of 15% was reached all patients who got there were then instructed to follow Australia's national dietary guidelines and to see a dietitian once every 3 months for the next 3 years.
Over that same 3 year period, everyone, regardless of whether they lost weight with Optifast quickly, or lost weight with Optifast slowly, regained the same amount of weight when following Australia’s national dietary guidelines – guidelines not even remotely designed for weight management or satiety (15% protein, 30% fat, 55-60% carbs) - while being provided with very little in the way of ongoing support.
Put another way, being prescribed a weight loss program that involves zero changes to lifestyle (aside from drinking shakes in place of meals), and then once weight is lost quickly or slowly, being told to follow a diet not designed in any way shape or form for weight management while receiving infrequent ongoing support, is clearly equally ineffective.
The fact that weight lost comes back when the intervention you undertook to lose the weight is stopped is anything but surprising, and yet that is precisely what was done with both the rapid losers and the slow losers. That there was no difference in their rate of regain speaks more to the authors' failure of recognizing obesity as a chronic condition, which like any chronic condition, returns once treatment is stopped, than it does to the speed participants lost weight using weight loss interventions that they were explicitly instructed to stop once their weight was lost.
The more weight you'd like to permanently lose, the more of your life you'll need to permanently change. All this study proves is that temporary changes lead to only temporary results and that what matters to your longterm success isn't the speed with which you lose your weight, but whether you lose your weight with a lifestyle that you enjoy enough to sustain.