Very true. It is ironic that an adult child must now tell a parent the things that my parents told me before I left home and went out on my own: "As long as you're under MY roof, you will not ..... (stay out all night, come home drunk, etc)."
To Rachel, the awkwardness might be alleviated if you simply tell your parents that you are not prepared to give them an explanation and that the items they found relate to a private part of your life that will remain private for reasons that are, well, private. Discussion closed. Then just enjoy your time with them. Let them come to whatever conclusions they like. If they insist on an explanation or if they keep bringing it up, you could tell them they are causing tension in your relationship by not respecting your privacy and if it continues you will limit your time with them.