You can watch movies stored on WD Mycloud device on your TV, but real life scenario would be that device is not directly connected to the TV as it should be connected to the router/network that you have in his premises, and then through video playback app on his Smart TV you can access device like Media server and play video content stored on it.

It all depends on your TV, what connections it has (USB? USB for data with disk) but I do not think, that this NAS has the desired features for you.