The Blaze also referred to the victim as “special needs” which is more euphemistic and vague than “mentally disabled.”
4 Teens Beat Up Disabled Man Demonstrating Polarization of the Internet
Emma Lindsay

I would guess that this might have something to do with the fact that Glenn Beck who founded The Blaze also has a daughter with special needs. Therefore, the term might be the preferred one within the company but this is only my personal guess and not a solid fact.