Also, based on the geometry of the xwave headset it looks like the electrode(s) are very rostral, so I would imagine that it picks up a lot of EOG from the eyes and EMG from the frontalis and corrugator supercilii (eyebrow muscles).

The ground, again from what I can tell from the photo, is on the earlobe. This is not a terrible place for a ground (there are no muscles there) but it's not ideal for removing EMG artifacts.