My recent experiences, perhaps a dozen times this year arriving into Narita has been similar to the OP. First off the plane, arriving on NH generally, and finding the terminal completely empty as well as zero people at immigration and near or zero at customs.

Love arriving on ANA since most pax are going into the Japan passport lanes. Further, being in F makes a big difference.

I never check bags. Came in a few days ago seat to exiting Narita in < 10 minutes by my approximation.

I've been coming out so fast recently that I've had to tell the car service to ensure the driver is there immediately at the time of the plane's arrival. No sense in waiting around after having everything so expedited!

Incidentally, zero lines at outgoing immigration at Narita earlier this morning. Seems late morning is a good time to be here since many of the TPAC flights go out in the mid to late afternoon.