I won't speak for Fester, but the meaning of nature is not a self-evident fact. Its meaning varies in scope according to preference.
The poster above just equated science with nature.
No, you are confusing natural (which is the word Fester used) and nature. They are not the same thing. Minimally, one is an adjective and the other a noun. Natural as applied to science has a specific meaning. Modern science is naturalistic and Fester knows what this means.