I'm sorry to hear the chick didn't make it :( They can look really strange in there sometimes, multiple pieces moving independently, I can see how it would be tempting to interpret that as being two separate chicks. I've noticed that there are often two areas of movement - the head and the feet...
Very cool! Will be watching to see what happens. There is a possibility it's not twins though, just two parts of the same embryo. Especially because the part on the right isn't as dark as the other one, and doesn't have a clearly identifiable dark black "dot" (the eye). I've had this happen...