Your friend is right and then wrong.

Yes, turbocharged engines usually have lower static compression ratio. For example my Subaru had 8.5:1. While NA engine is typically 11 to 13. But why ?

To compensate for higher air pressure from turbocharger. To make more force you need more pressure that comes from explosion. By forcing more air in, you can add more fuel and generate more pressure.

Turbocharged engines tuned for performance need better octane fuel, because you are trying to compress air that is already compressed, meaning that temperature raises more quickly.