Search for "Zero-overhead abstraction mechanisms".
If you read it you will see Bjarnes goal was to provide the highest level of abstraction possible at "zero overhead". At the time he was creating the language, OOP was the newest and "highest" forms abstraction around... problems with it as an abstraction weren't as evident back then as they are now.
But yeah, I agree that you can make an argument for RAII and templating being the main differences over OOP. But Zero cost abstractions are not a side effect at all.
Source: https://www.stroustrup.com/ETAPS-corrected-draft.pdf
Search for "Zero-overhead abstraction mechanisms".
If you read it you will see Bjarnes goal was to provide the highest level of abstraction possible at "zero overhead". At the time he was creating the language, OOP was the newest and "highest" forms abstraction around... problems with it as an abstraction weren't as evident back then as they are now.
But yeah, I agree that you can make an argument for RAII and templating being the main differences over OOP. But Zero cost abstractions are not a side effect at all.