I think it was definitely Latias that kissed him.. because think about it, not only did it seem more like Latias, but if it WERE actual, human Bianca they wouldn't have gone as far as kissing. It's Pokemon.. there's never kissing between two humans/main characters in Pokemon.
Not poking holes in "It's Latias" theories, but it seems a lot of people forget about this...
Latias kissed him on the cheek. Melody (human) has already done the same thing.
https://www.youtube.com/watch?v=K0uKMjulU7Y
So I think they actually have a problem with a pokemon (or in Pokemon Form) kissing him on the cheek as opposed to having a human kiss him. People who HATE PokemonxHuman shippings don't really have a huge problem with Latias because a humanoid form, even if she REALLY is a pokemon, doesn't seem as offensive.
What is it? Altomareshipping? I don't remember. I like to type Latias for some reason so I never needed a reason to learn it.