To further explain...
There is an "SBS mode" on the buses, but depending on the bus, it's actually labeled as such.
A simpler definition would be rear door mode. I'l break it down:
Passenger controlled
The regular way the back doors are controlled. Once the driver turns the door handle to rear, the back door(s) unlock and the passenger pushes the door open themselves. Usually they would slam back closed (Novas not included) unless someone pushed the tape/bar/strip in which they would stay open until the driver puts the handle back to close.
Driver controlled (SBS mode)
In this mode, once the driver turns the handle to rear, the back doors (the middle door on the artics count as a back door lol) open automatically and stay open until the handle gets put back to closed. Depending on the bus, it' called something different (touch tape bypass on the RTS, SBS mode on the Novas, etc), but it's all the same thing. Buses doing SBS routes (and to a lesser extent shuttle buses) are supposed to have their buses like this.
All it takes is a simple flip of a switch on the driver's panel. In your case, the driver turned the door handle to where the front doors would only open.
But like B35 said, that still doesn' stop people from yelling at the backdoors to open lol