it could be some sort of nightmrare that she is having of them taking Henry away.
This is exactly what I thought. Just the way the charmings are standing with blank faces reminded me a lot of Reginas first nightmare of her tied to the tree. Also, this might be a minor detail, but when Regina throws Emma back, i noticed that charming is only protecting Snow and not Emma, when Snow was not in danger of Regina. And knowing charming he would probably throw himself in front of Emma. This is also why I think it could just be a nightmare. But i might just be reading too much into this, I tend to do that.
No, I think you might have something there. My first thought after seeing that clip was that it was a nightmare as well. The clothes and the setting of the scene just seemed all too…odd.