Lockhart was by no means a competent professor. He always loved wasting large amounts of time and energy on posturing, trying to use it to attract more students' attention.
For instance, just a moment ago, Lockhart had waved his wand left and right, attempting to make it perform some complicated trick, and then... he accidentally dropped his wand onto the floor, causing an awkward silence to fall over the room.
Albert even caught the sneer hanging on the corner of Snape's mouth. Clearly, the Potions master was well aware of Lockhart's true nature and held him in absolute contempt.
Chapter 531