He's only seen Edward a couple of times and feels that he doesn't really know him at all (as per Barbara's quote below). He knows that Edward is a good friend of the family - almost part of the family - and has undoubtedly heard that he stayed with them when he was in the area.

Elinor is, to my mind, the perfect person to tell him about it. She's rational and articulate and kind and compassionate. To everyone's mind, if Elinor is telling you the news, you can depend on it. She doesn't fall into romantic flights of fancy like her sister(s) or mother.