As far as my cooking experiences extend, a traditional mousse does not contain gelatin or any other artificial setting agents.
(The best chocolate mousse I know of doesn't even contain cream--Allow 1 egg and 1oz of chocolate per serve. Whisk 1 egg yolk with 1oz melted chocolate until thick. Carefully fold through a stiffly beaten egg white, pour into a serving dish and allow to set in the fridge.)
A bavarios is cream, fruit puree (or chocolate or some other ingredient), and just enough gelatin to set without turning it wobbly or rubbery. The texture should be silky.
So, in short, I guess the difference between a mousse and a bavarios is the ingredients, traditionally speaking.