It depends on where you live. His music is still under copyright in the US, and is public domain pretty much everywhere else (EU, Canada, China, etc.), though I am not sure what law is in effect in the UK after Brexit.
pianostreet owners are from EU, and it is probably hosted on EU server, therefore for them it is public domain, and they can keep it on their site legally, but if you are in the US you should not download it.