Someone started that rumor and others just started repeating it without any facts to back it up. I am certainly no George Soros fan but it makes people look like conspiracy nuts connecting him to this.
I don't know if you're old enough to remember the John Birch Society of the early 60's, but this is EXACTLY the phenomenon that happened with that group. Thankfully, intellectual conservatives like William F Buckley fought against that insanity and the ludicrous conspiracy theories of the Birchers, and purged them from the movement.
For whatever reason, we've seen the same conspiracy theory phenomenon take root again.