well they really don't know Harry Potter like the back of there hands. Yeah they may know that Ginny and the rest of the Weasleys and Hagrid mean alot to him. But they also think that Luna means just as much as Ginny and the rest of the Weasleys, becuase they don't know harry like a freind would know harry they only know what they are told about harry, they are told that Ginny and the rest of the Weasleys mean to him, and Hagrid are really close and they are also told that Luna is really close too, in fact they once dated.

and they wont kill Ginny and the rest of the Weasleys mean to him, or Hagrid becuase they are smart and will not put them selfs in danger, but Luna on the other hand she is dumb as nails she will walk right up to a death eater and ask for directions.