As far as I know there is no intentional difference. Adrian tried it out and it seems to sound identical to the neck only setting. When Mo gets back I will ask him what the circuit is doing.
I work with Nordstrand on their social media. I pop on here every now and again to help answer any questions. Be sure to tag me with your Nordstrand related queries!
Several videos here. Check out the video by Jonathan Herrera. He has summarized the pedal extensively. https://nordstrandaudio.com/products/starlifter-bass-preamp-di