"No direct link existed between currently depressed mood and either creative interest or creative behavior. These results suggest that the association between depression and creativity is solely the result of rumination."
As to his second paragraph on "preconditions to be creative": Again, no. Amabile (1983) in "The social psychology of creativity" postulated three components of creative performance: (a) domain-relevant skills, (b) creativity-relevant skills, and (c) task motivation. Yes, you may need sufficient knowledge in a specific domain to increase your chance of acheiving creative "eminence" within it, but it does not preclude you from doing so if you are not an expert. One must understand the science of creativity before they can say they have creativity-relevant skills, which this author unfortunately does not seem to have.
Creativity, in most experts' views, is generally the marriage of novelty and usefulness. In order to accomplish something creative, one must go through a process of divergent thinking, to create many varied options, then convergent thinking, to narrow down the options that make the most sense, or fit the challenge (even if the challenge is only how to create something that is new and useful). Both in divergence and convergence, incubation is a very useful tool, but it is hardly essential in every creative process. So, no, creativity does not require isolation. However, it is my contention that imagination (divergent ability) may flourish when one is disconnected from the "outside world" for some time.
edit: grammar
"No direct link existed between currently depressed mood and either creative interest or creative behavior. These results suggest that the association between depression and creativity is solely the result of rumination."