Xperia is just a brand. Being or not an Xperia does not make a difference if the phone looks and feels like one, even if it does not use that brand.
That being said, Live With Walkmen is the only SE Android phone that is not called Xperia. But you can find Xperia fatures (Facebook Inside Xperia, for example) and contents (ringtones, for example) using the Xperia name. So yes, I would say it's an Xperia.
