What do you think is meant by “Abstract photography can be defined as capturing images in which the subject isn’t the most interesting element”?

I think that it means that abstract photography does not need to follow the rules of photography. The photographer can bend and break rules to create images that are considered abstract. This leads to images being created that look wrong but have a unique feel to them. For example, the photograph by Uta Barth uses blur to confuse the viewer so that they don’t know where to look. there is no clear subject which makes the photograph interesting.

No, you cannot take a wrong picture. Every picture has own unique style that adds to the photograph and it does not need to follow the general rules of photography.

No, context is not important in a photograph because the context shapes what the viewer sees. if there is no context then the viewer is free to interpret whatever they might see in the photograph. When I first saw the photograph without the wrong I didn’t realize  that there was anything different about it. But when  the image expanded and revealed the wrong I looked closer at the image and noticed several things “wrong about it”.