You can access creative mode on the Demo Version.

Put the summary of the bug you're having here

What I expected to happen was...:
it would say to buy Minecraft to access Multiplayer.

What actually happened was...:
it let me access multiplayer without owning the game and let me even set creative mode.

Steps to Reproduce:
1. go into a demo world
2. go to the pause menu and click open to LAN
3. switch gamemode to creative and press start LAN world