While little Alex called his fellow "ultraviolent gang members' his droogs, it wasn't because they were "ultraviolet gang members". It was because they were his "friends" or "mates", in as much his little sociopathic self could have friends.
Giving the meaning of "droog" over to "ultraviolent gang member" is just this dope connecting dots, not defining the term.
That's the derpish way, and not very horrorshow, you ask me.