The single player game on Windows 10 does not pause while viewing Game menu after pressing ESC. The environment continues on leaving the player open to get attacked by enemies and lose hunger.
1. Create or enter existing Single Player world.
2. Survival or Creative game modes do not matter.
3. World type (normal, flat, etc) does not mater.
4. Press "Esc" while in game to access Game Menu.
5. Observe that the world environment is not frozen but actually continues on normally.
6. Animals and enemies can be seen walking around unaffected in world.
7. Time passes (sun rises and sets) normally.
8. Your hunger bars deplete normally over time in Survival causing you to eventually take damage.
9. Return to game later and attempt to recover from affects of you not placing your character in a safe place from enemies and/or not eating food while away from keyboard.
10. Imagine if the Windows 10 edition would be similar to the Java edition where the pause status actually pauses the world while viewing the in game menu.
For now, this is working by design.