Passenger side air bag light

Stupid question- I very rarely have a passenger in my 2016 Tacoma TRD Sport, but today I noticed the Air Bag On light coming on when a friend was seated, of course wearing the seat belt. It went off as soon as I dropped him off. NORMAL? I read the manual but am still a little confused. I must be DENSE. It didn't make sense to me- why have a light come on indicating the passenger side air bag is on but no indicator showing the DRIVER side air bag being on?
Can someone please clear this up for me? I'm still under warranty.

 

Its normal, there is a certain weight requirement so not to go off If a child is seated there

 

Thanks for clearing that up!

 

The owners manual will help.

 

The driver side airbag is always on.