There are only two reasons why alpacas smile a lot: they are happy or their facial anatomy gives us the impression that they are smiling. If they smile when they are happy they are like people which would be unusual. My strong suspicion is that alpacas smile because their faces are made like that. They probably smile all the time or a lot of the time and all of them can’t be that happy all the time. They probably wear a fixed grin as we say and it reminds me of Grumpy Cat who had a fixed grumpy expression not because she was grumpy but because her anatomy was made like that. It gives a false impression.
In the cat world, which is a world I know well, any cat who smiles is smiling because their face is made like that at least predominantly i.e. it is their anatomy. It does beg the question whether animals can actually smile in expressing joy and happiness. Sometimes I ask that question of my cat because sometimes he appears to smile although it will be an incredibly faint smile.
As to emotions, animals do feel at least the basic emotions such as contentment, unhappiness, anger and fear et cetera. Whether they can experience guilt and shame and so on is another matter and that aspect of their emotions and behaviour is work in progress for humans.