Welcome to Android Central! Albums in Google Photos are virtual constructs -- i.e., the file remains in the /DCIM/Camera directory, but Google Photos knows you created Google Photos album that includes this photo. That album is part of Google Photos, so if you go to photos.google.com on your computer browser, you'll see the album there as well, and the photo will be part of it.
If you physically created a new directory on the phone's Internal Storage and then moved the photo file to that directory, then it will show up in the Device Folders section under that folder. But that isn't the same as a Google Photos Album. So the question here is if you remember physically moving that photo file to a different directory on internal storage, or if you created an Album within Google Photos and assigned that photo to be in that album.