Others have mentioned that there is indeed a "free roll" mode and I'm prone to think your hypothesis regarding the implementation may be correct. The specifics, however, do not matter to me.

What I'm wondering now is, if "free roll" mode is activated while I'm at a red light... is there a chance I start rolling as I do in my manual when I take my foot off the brake?

Maybe I should just reach out to Tesla at this point though (-: