Yes, sorry, the Audi auto lock feature is speed related, l believe once you reach 5mph or thereabouts.
The only time related auto lock lve come across is if you unlock the car using the remote, but don't open the door, then it relocks automatically after about 30 seconds. I don't recall their being an MMI setting for this, sorry.
On my previous cars (and current S7) this has been enabled by default.