It's never been stated [yet] how the anime interpreted Eevee's evolution to Sylveon. The games require two affection hearts in Pokémon-Amie plus a Fairy-type move. I would assume if the Eevee is affectionate enough (through more conventional means) and it knows a Fairy-type move, it would evolve to Sylveon; noting that affection is different to happiness (for Espeon and Umbreon).

It has been stated that Eevee had started evolving to Sylveon outside of Kalos in an earlier post.