Recent versions of Photoshop have changed the way that users save files:
When a user tries to save a file, they will see three options – Save, Save As, and Save a Copy. If you choose either of the first two options, Photoshop assumes that you want to save it as a file type that preserves layers. It will only provide you with a limited number of file types from which to choose.
One of those is JPEG 2000. This is not your typical jpeg format. If you want to save your image as a normal jpeg file, you need to choose the option Save a Copy. The list of file types provided will include the normal jpeg file type.