It's a Dual Layer game.
R3OE01 - Metroid: Other M = 7.26GB
This is a list of all the other Dual Layer Wii games...
-Metroid Prime Trilogy
-Raving Rabbids Collection
-Sakura Wars: So Long, My Love
-Samurai Warriors 3
-Samurai Warriors 3 Xtreme Legends
-Super Smash Bros. Brawl
-The Last Story (US & EU Only)
-Xenoblade Chronicles (US & EU Only)
The only way that I know of, to physically see if the disc is dual layered or not, is to look at the back of the disc's directly. Regular Wii DVD's will look silvery. While the Dual Layered Wii DVD's will have a goldish tint to them. You may need to have two of them side by side to tell the difference, and be in a room with plenty of light.