No, it is neither.
Under Japanese law as of 2023, authors cannot relinquish their copyrights and put them into the common property of society (authors cannot put them into the public domain).
In other words, even if a music distribution site operating in Japan declares that its product is “copyright free”, it is still in a state of “the author owns the copyright, but it can be used free of charge under certain conditions”.
Therefore, the songs that are distributed on this site are neither “copyright free” nor “in the public domain”.
Please see the Terms of Use for details.