These seem about right. Snowboard levels are really hard to define. Skiing has a clear, established progression. Snowboarding only has a somewhat clear progression up to level 3-4 on that chart because everyone needs to know how to link turns on green terrain. After that, things start to get a little fuzzy.
At the level 4 stage in that chart, you could have 5people in your level "4" group, all with different goals. One could want to learn flatground tricks, one steeper terrain, one carving, one switch....
This complication is one of the reasons I love snowboarding and love teaching it.