Okay, calced it real quick to give you a rough estimate. The dimensions of the ice cube look to me to be roughly...
14 m long, 6m wide, 10 m tall with reference to Phoenix Man, who I assumed was 2 meters tall. That's how I calced it in a ellipsoid calculator and it's probably not quite that big...
4/3π * 7 * 3 * 5 = 439.82 m^3 for volume,
Density of glacial ice is 917 kg/m^3,
439.82 m^3 * 917 = 403,314.94 kg, Class K,
If I underestimated the volume it could potentially be Class M. If you could find a denser material that it could plausibly be, then it would certainly be class M because even glacial ice is less dense than water. For instance, if he were tossing a ball of concrete or steel it would be class M. Worth calcing, I would say.