Functionally, the two locations are identical. The main difference is that drawings in iCloud Drive sync across your devices and may show a status icon under their thumbnail.

• Not Downloaded: A cloud icon indicates the drawing is in iCloud but not downloaded to your current device. To download it, tap to open it, or Tap+Hold the drawing and select Download.
• Downloading/Uploading: A progress circle appears while the file syncs with iCloud.
• Downloaded: A drawing fully loaded on your device has no status icon. You can free up local space by Tap+Holding the drawing and selecting Remove Download. The file remains safely in iCloud Drive.