A composite is a mixture of a bunch of stuff to make something else. :P
Plywood is considered a composite, for example. The "glass" screen on my iPhone 4 is also a composite.
If it was just glass, you'd get all the "wonderful" reflection properties of glass.
I did call Sony today, and they told me "it's not glass or plastic". I still personally call it a plastic though.
Also, if anyone's looked at their NX810 from a way off angle while it's off, they'll notice the screen isn't completely flat (smooth?). Not glass unless they're using 1870 technology to make the stuff.
I've never seen an NX810 and LX900 side by side so I can't make an honest opinion between the two but I liked the specs of the NX810 enough that I bought one of them instead of an LX900.
If you look at some of the pics ppl have posted of the 810 you'll see that rainbow effect from the material on the front of the TV. Glass doesn't do that, it's a result of whatever stuff Sony mixed together to make the anti-glare stuff that's covering the front of the TV.
Just to mention it, if I tap on the screen of my iPhone 4, and the TV. It makes the same sound. The glass covering the photos in my house, windows, etc all sound much different.