Turbocharged engines generate more heat due to increased combustion being smaller engines to produce equal or higher performance than equivalent naturally aspirated. You can't compare a NA with turbo/ forced induction engine.
Turbo needs high octane for the fact that if lower than required fuel grade is used , it will ignite sooner than it should in chamber.. and result will be knocking over time.
Yes your R18 ran on regular fuel because the engine dynamics are diffrent than a turbocharged engines. Again I am not an auto engineer or expert and share what I learnt reading diffrent resources. Someone shared a good example somewhere here in this thread.. most of JDM Kei cars have small turbos and people have issues overtime with knocking and fuel consumption and economy.
I congratulate everyone who are buying Civic X.. but follow what the manufacturer or dealer tells you.
Don't listen to people who tells you according to his/her experience