It also means when the companion dies or is removed for whatever reason the Hunter is now the one doing the 'Hulk Out' but he's not getting some eidolon shell he's just evolving his own flesh.
we're not calling up an eidolon we're just making the animal companion 'Hulk Out'. Now unless I'm completely mistaken this ability is ONLY granting the evolutions the same as if a summoner was able to cast Evolution Surge on something other than his Eidolon. Just having a little look over this thing and in some respects it seems superior to the summoner synthesist.