I don't think you've missed anything. The news here appears to be that a unsecured public proxy is willing to proxy things and make them available to the public

I don't think you've missed anything. The news here appears to be that a unsecured public proxy is willing to proxy things and make them available to the public in an unsecured fashion. The article does make the point that some monitored networks might trust golang proxy URLs more than arbitrary web URLs and that this could be used for bypassing reputation filters etc -- but there are already several ways to do that, and this one doesn't seem particularly special.