You must understand that console game development is not alike PC game development. You have to taylor your APIs to your machine in order to lift all the performance issues you may find. Adapting a standard graphic stack (with all its genericity whose goal is to fully abstract a large number of very different hardware) is not a good thing. It's even worse, since the devleoppers will want to have a fine-grained control over the hardware (that's why they added a special tag on the APU/GPU shared L2 cache cells ; this tag allows the developpers to control cache invalidation).
Now, on the use of FreeBSD, it makes sense : Sony has a good knowlegde of MIPS OSes (MIPS were used in the PS1 and in the PS2), PowerPC OSes (through the Cell processor used in the PS3) yet it doesn't make sense for them to build yet another x86_64 OS from scracth when there is already many open source offers. The license of FreeBSD is specifically targetiing these needs - allowing a hardware vendor to adapt the OS to its specific needs without being forced to release their patches in the wild (you may or may not disagree on the philosophy yet that's the goal of the 3 clause BSD license).
It doesn't mean that Sony is all clear here. The system probably use may GNU bits (including the C and C++ runtime if the screen captures are genuine) so it might be possible to ask them for some information on the subject. I suspect the GPL enforcement organisations are already looking at this subject (and if they don't, may I respectfully suggest them to do so?)
(for those who believe that Michael served us yet another rumor - yes, it's true. Yet the rumor itself is traced back to VGLeaks, the guys who published the very first technical information on Durango (XBox One) and Orbis (PS4), showed us the first pictures of the Durango development machine and so on. It seems they are more reliable than CNN. In this case, they backup their claim with screenshots of the developpers boot screens. Since we're not April the 1st, I believe this story to be quite true. YMMV)