You fail to understand methodological naturalism. It does not set a boundary on what DOES exist, but on what can be *scientifically* determined to exist. That is why is is "methodological" - it is about method, and it's limits, not about absolute truths.
And much of what creationists claim *is* within the bounds of methodological naturalism. For YECs there is the age of the Earth - only the "apearance of age" argument escapes that, and that is generally unacceptable to most YECs on theological grounds. FOr those who believe in a literal world-wide flood that can be investigated naturalistically (and it has been found that it never happened). We can also test relationships between life through taxonomic and genetic evidence and that supports evolution over creation.
That God created life is outside of science. That all life evolved from a common source rather than representing a series of seperate creations is not.