It is written in C++ and I did not see anything that looked particularly heavyweight. Unless there is something unusual happening it should run fine on a raspberry pi. I think a big motivation behind someone doing a stand-alone like this is precisely to get rid of mountains of dependencies they don't need. Small footprint means better performance and arguably small amounts of increased percentage performance on facebook's massive infrastructure is more important than it is on a small device like the raspberry pi. Small savings are multiplied many times over on a huge system like that.
My attention is directed elsewhere but I may at some point pull that stuff down, compile and give it a whirl.
I am still a little bit hopeful that facebook will turn into a good player. Their monstrous privacy invasion and erection of a walled garden was basically a necessary self-defense against encroachment by another player. They are large now and the dynamics of group forming networks makes them enormously powerful and qualitatively different from a smaller version of this type of network. However, I still see some vulnerabilities and given the value of maintaining their position (I write elsewhere about a facebook financial 'singularity') you can't fault them for playing things close.
To the extent that facebook has had the latitude to do good things without self-immolation they appear to have done so. Time will tell. My instinct is that these gigantic organisms are intrinsically evil, but this recent open handed release of code is a hopeful sign.