Welcome to Android Central! What device do you have? Can you show us a screenshot of the Settings>Storage screen? Are you sure you moved the pics/videos to the external SD card, since some phones partition internal storage into app storage and "internal SD," which can be confusing?
The other thing to remember is that thumbnail databases can take up a fair amount of space, if you're used to having a lot of photos stored on your phone. Use a file manager app and look at the /storage/sdcard0/DCIM/.thumbnails folder, and see how big it is. Mine is 660 MB, and I don't even have any photos stored locally right now. The thumbnails can be from all of your cloud photos, as well as any photos you may have taken with your phone.