QNX does provide a DBus implementation (based on the Linux one, so not a full reimplementation or anything) as part of the larger userland package, but it's in no way a core component of QNX itself and as far as I remember not used by any of the other services it ships with, so its purely there in case someone wants to use it for their application, e.g. because they also have a Linux version and don't want to use QNX-specific APIs if they can avoid it.

So yes, that was just a choice of whoever made the Jeep infotainment system.