And: how can you tell the pig is happy? Just because it is eating and moving? Popcorning they often do in a situation when they are happy, but they also do it when they are stressed.
Our neighbor years ago did a really bad job taking care for her pig, it lived with a rabbit, in a cage too small, fed hay only like when she was in the mood, they were lifing outside and the cage not properly isolated- that pig still lived and ate and run around and didnīt look unhappy (what is a unhappy pig supposed to do by the way? The only thing it could do was to stop wanting to live. But they do have a strong will to live.)
And if critisized my neighbor would tell me that pig was happy too...
Of course, you could ask me the same. We canīt ask our cavies. But I do everything I can to keep them as species appropriate as I can. As they life in herds of mixed genders in nature I try to keep as close to that as I can.