That makes perfect sense.My guess is Moldvay didn't want to take up two different lines for Tolkien, and probably considered LotR an adult work, so he included The Hobbit along with it in the Adult Fantasy section.
Drifting back I was wondering about the animated movies and looked them up. The Hobbit and LotR released in 77 and 78. We never saw them on our home TV, but at some time in the 1980s WGN had them on semi-regular rotation because I remember seeing them at my grandparents a few times.