David,
There are several ways of measuring height, as you've found out. So, paying attention to exactly what's said is a very good idea. Mast height usually means exactly that, how tall/long the mast is, and is usually measured from the deck. Boat height usually means the mast height and the height of the hull above the water line, sort of. It can also mean from tip of keel to tip of mast. Just depends on how and why it's being stated (more 'pay attention' time). Confusing? It certainly can be - lol! Have fun...
- 'Doc