It is his hand. I was curious to know for sure myself now so I took a screen shot into Photoshop and zoomed in. It's 100% a hand with a lightsaber. Though it's not gripping it. The hand is open falling in beside the hilt of the saber. Afterwards I stumbled on this-

http://scifi.stackexchange.com/questions/8053/is-that-lukes-hand-falling-down-at-the-end-of-the-empire-strikes-back

My screenshot actually turned out clearer than this one, though I don't know if it's different because mine is from the special ed. It also really looks like his left hand which is curious.