I never read it as outright "right = racist", but more of a right = more interested in systems than people.
Right wing politics is founded on the idea that caste systems exist and are both natural and proper. Left wing politics is based on the concept of equality.
The "left" and "right" comes from the French Revolution, where those on the right were for the monarchy and those on the left were for reform.
Which is to say, when someone identifies themselves or others it rarely follows the classical concepts.
So yeah, if we're getting technical, being right wing supports a system of inequality, which racism can be an example.
I'd never say that anyone right leaning is automatically racist in a burning crosses on the front lawn sense, but if they know what they're talking about, they're at least amenable to the concept that not all people are equal.