No need to be confused. That is exactly how I would have done it if you had not specifically entitled your post as you did. Solving quadratic equations should not be confusing, since there is ALWAYS a way to solve them - and rather simply at that. However, when there is an even easier way, it might be wise to use that easier way.
Normally, one would "Complete the Square" to solve such a thing. (Or use the general completed square known as the Quadratic Formula). In your problem, the square is already completed, so why undo it?