No one really knows. What definitions have been given are contradicted by the fact that incels used based to refer to pretty much everything.
I would also, on another note, like to talk about something from the Wikipedia article the quotee linked.
For several years the brothers had been embracing neo-Nazi culture, though this had escalated in the months before the killings, with them going so far as to tattoo Nazi slogans on their foreheads.
So now, doing life in prison, they will not actually be members of the Aryan Brotherhood, or at least couldn’t be at the time. Why? Because one of the rules AB had was NO FUCKING NEO-NAZI TATTOOS IN VISIBLE PLACES! In fact, they didn’t really think much of any visible tattoos, because when you get on the streets it limits the jobs you can get. And the Aryan Brotherhood, even being violent, racist Neo-Nazi fucks, were smart enough to know that to be successful, they also have to blend, and having their members able to fill various positions in any kind of business means those members now have access they wouldn’t if basically all the can do outside of prison is hang out in a Neo-Nazi clubhouse.
So yes, I guarantee you the AB members they wanted to hook up with told them they’re worthless fucking idiots who add nothing to the Brotherhood.