The 1.4TFSI CAVG is a crazy thing... despite all its flaws (like broken Turbochargers or broken chains) its a clever engine.
The cylinder block is made out of cast iron do withstand the combustion pressures - however the lamellar graphite cast iron is not as hyper as it sounds. It just the easiest and cheapest cast...
Topend is rather standard - 4V DOHC Aluminium Head with VVT. Nothing fancy or special.
The aspiration is where stuffs getting really crazy! A roots charger and a normal turbocharger booschting the engine - but not on the whole rev-range... which goes from 0 to 7000RPM. The Roots always operates... until 2400RPM, then it gets 'turned off' and can support the Turbocharger till 3500RPM if needed - you know, to dampen the turbo lag.
So whats going on in that strange thing!! On low load - there is no charging at all, the Roots is disengaged by clutch and bypassed, and the turbo is being bypassed - no booscht

On some proper load (like accelerating) the roots enganges till 2400RPM and is booschting with little help of Mr.Turbo to 1.5bar/21PSI - from 2400RPM till 3500RPM the supercharger is being disengaged at lower loads, and Mr.Turbo will do the job.But if you floor the pedal, the supercharger will engage again to supress any Turbo-Lag.
But at around 3500RPM the roots is being disengaged again and totally bypassed - because the turbo will always be at maximum possible boost at every situation and the turbolag wont be noticeable. However the pressure drops to max. 1bar/14PSI.
The roots blower can build up 0.75bar/11PSI and is regulated with the magnetic clutch and bypass flaps - theoretically the roots could run all the time, but thats not intended by VAG.

Here the boost pressure preview

And because VAG thinks that people dont like the roots whine - they muffled it. It also could need more booscht - roots all the way would be interesting!