Yang's likely going about this the wrong way.
The American political system makes it pretty easy for motivated people to have an outsized impact on primaries. A third party is based on the idea that you would somehow have more appeal to a much larger group of people when you couldn't get a much smaller group to have an impact in primaries.
A smarter way to push for reforms would be to support nonpartisan initiatives and/ or endorse candidates who meet particular ethics standards. This way you're not as offputting to the majority of voters who are partisan.