Hello P7th0n,
Thanks for using Apple Support Communities.
From your post I understand that you're trying to create a movie in iMovie on your iPod, but you're getting a message that the movie is still downloading. This indicates you're using iCloud Photo Library, and have the Optimize Storage option. This keeps a thumbnail version of the movie on your iPod, but will download it when you play it. This requires a data connection, and in your case, a Wi-Fi connection.
If you turn on Optimize [device] Storage, iCloud Photo Library will automatically manage the size of your library on your device, so you can make the most of your device's storage and access more photos than ever. All of your original, full-resolution photos and videos are stored in iCloud while device-size versions are kept on your device. You can download the original photos and videos over Wi-Fi or cellular when you need them.
If you turn on Download Originals, iCloud Photo Library will keep your original, full-resolution photos and videos in iCloud and on your device. Download Originals is the default setting for iOS devices with the free 5 GB storage plan and for all Mac devices.
You need an Internet connection to access an original photo or video that’s stored only in iCloud.
iCloud Photo Library FAQ
Take care.