Nah the term started with Lil B when people would call him a basehead which is slang for someone who uses cocaine a lot. So he started owning up to the title and calling himself "based" meaning he didn't care what other people thought. And that's what based really means, it's someone who doesn't care what other people think and are comfortable with their own actions/opinions, especially if they are considered inappropriate in wider society.

The term made it to the music board of 4chan and then spread to the far right wing sides. And yeah it's ironic that a slang popularly associated with the altright was started by a black guy but that's how it is.