It actually hasn't, apart from the fact that they both are based on an real-time kernel. Symbian has it's roots in Psion's EPOC16 and EPOC32 operating systems, and in fact wasn't a real-time os before the introduction of the EKA2 (EPOC Kernel Architecture 2) kernel in symbian 8.1. Blackberry uses QNX, which has been an RTOS since it's beginning and shares no roots with either EPOC or Symbian. The chart is a bit misleading in this respect.