No, buckwheat is not a grain. Contrary to its name it is actually a seed. More popularly known as pseudo-cereals or pseudo-grains. Buckwheat is similar to amaranth and quinoa which are also psuedo-cereals. Just be careful for cross-contamination with other grains. It is quite delicious and gives you that fix when you are in need of some high carb food ;))
And thanks Farmwife for the cookbook info!