2.9.4 Compound Commands
The shell has several programming constructs that are "compound commands", which provide control flow for commands.

Each of these compound commands has a reserved word or control operator at the beginning, and a corresponding terminator reserved word or operator at the end

でその後Compound Commandsとして上げられてるが以下の6つ
- Grouping Commands
- The for Loop
- Case Conditional Construct
- The if Conditional Construct
- The while Loop
- The until Loop

echo helloは開始・終了を示す予約語もなければ、上の6つのどれにも当てはまらないからCompound Commandではない