People refer to this electric compressor as a 'turbo' and that includes Audi themselves. However, an electrically driven compressor wheel is essentially an electric supercharger. The advantage is that you do not have to wait for spool from exhaust gases but that the wheel with electricity can be spun to maximum right off idle. The idea is to eliminate lag from the turbochargers which is vital in low revving diesel applications.
The electric compressor helps throttle response and off the line performance. Once the conventional turbos are spooled the electric 'turbo' is disengaged and bypassed. The question remains on how Audi intends to power the 9 horsepower electric motor spinning the wheel and where that energy will be stored. The engineers will sort all of that out.
The diagrams below help explain how the idea works.