I think it's in issue related to icloud drive. I do not have problem renaming a file if it is stored "on this iPad". The issue arise when storing file in iCloud Drive. I tried to restart the iPad and it does not help. I have reproduced it on two different iPads. Here are steps to reproduce it:
1. Turn off WIFI (and data if you have)
2. Go to Artstudio Pro, create a new document in iCloud Drive.
3. Navigate back to the gallery, long hold on the newly created document.
4. The context menu pops up, however, it is the short menu (shown in the screenshot at the original post), instead of a regular long one. It does not have delete or rename options.
Note even when remaining offline, if I open the iCloud Drive with the iOS "Files" app, I'm able to long press and rename or delete that file without the issue.