Different people have different definitions of high-key photos. I remember posting that the
epitome of a high-key photo is one in which the dynamic range is roughly mid tones to the bright tones. Someone immediately responded that lots of high-key photos have deep, rich blacks to contrast with the other tones. I still think the epitome of a high-key photo is exemplified by the photos that Colin posted, though I understand that there is a larger range of styles that can justifiably be considered high-key because the concept is more subjective than objective.
Christina,
The bold font is used by me to bring your attention to the word, "only." The histogram shown below is of your photo.
Moreover, you have developed your skills enough to know that the dark tones of your image couldn't possibly be displayed on the far right side of the histogram unless you don't understand the data that is indicated by the histogram. You might refer to my recent post that you liked that explains the Curve tool. The details of the horizontal and vertical axis that pertain to the Curves tool also pertain to the histogram.