How do Soundraw know for sure the auto-generated music is original and therefore royalty-free? So not close enough to an already released, copyrighted, piece of music.
There are 35 million released songs. Completely original music is a myth. If it doesn't use samples without a proper license, then it's legally OK.
Currently, US courts disagree.
Given that not even an artist who handcrafts the whole song does know for sure I'd say they don't. They just use generic enough loops that the result is also too generic to run afoul of someone
Alot of music from previous century is just classical music playing somehow different. For example using Beethoven symphonies backwards.