The SC usually will not push a firmware update unless there is something else wrong with your car. Basically, once Tesla issues you a service ticket, your car gets priority for receiving updates (since those can resolve some customer issues). If you are also on the service wifi, you'll get your update staged while they perform whatever work.
The current software update process is that Tesla chooses customer vehicles in batches and pushes the update (stages). Sometimes these batches are for particular hardware because the firmware fixes those (i.e. RHD drives, or AP2.5 or smart air suspension). Increasingly rarely these dates, they are general firmware pushes (.42 was the last one, 50.1 could be the next but it is still not widely distributed).
There is no actual rhyme nor reason.
Congrats on your new car! If I see you, I'll be sure to wave. AP makes that so easy!