Security lockout?

Audi security systems are some of the hardest to work with. You say he had steering issues? What were those issues? I'll assume he just installed the steering module without doing any programming or anything else? I would first verify that work, IE are the wires actually correct, that is because the correct module should have been a plug in part with no rewiring needed. Rewiring suggests that isn't the correct part which may have different control parts in it that do not work with your current vehicle, so it locked out the system.

IF the module itself is correct it would need to be programmed using a VAG capable programming tool and a factory programming link with security code from a dealer or NASTF registered shop before it will program anything in the security system. They are not DIY friendly at all. Then once it is programmed in, you can deal with getting the ignition cylinder to work by programming the keys into the replacement module. AUDI and VW have some of the toughest anti-theft systems to deal with when it comes to repairs.

So the question is it possible that a VDC cable is the only thing that can communicate not regular scan tools?

A standard tool should talk to it at least. What scan tool do you have?