Straight from Wiki: Forced induction is the process of delivering
compressed air to the intake of an internal combustion engine. A forced induction engine uses a gas compressor to increase the pressure, temperature and density of the air. An engine without forced induction
READ:COMPRESSED AIR is considered a naturally aspirated engine.
https://en.wikipedia.org/wiki/Forced_induction
You posting the definition of the word "forced" is completely out of context for this discussion.
Lets look at a single cylinder with the piston in BDC. You have .500 liters of cylinder displacement. Lets say we have a nice even 20% oxygen content from the atmosphere. If you add nitrous, you see an increase in oxygen to say 33%. Your cylinder volume is still .500 liters. The volume didnt increase, just the oxygen content did. If 50% of your cylinder volume is now your nitrous mixture, that means you had to displace 50% of that volume of atmospheric air that normally would have been there. You arent ADDING volume, just substituting volume with different constituents. You cant increase the internal volume beyond your .500 liter displacement WITHOUT compressing the intake air first.