i believe this in only a rumor and facebook wont ever create their own crypto because facebook has been a hater for cryptos . they ban crypto advertisement and post or even crypto related accounts . i also see that facebook has already have thier own electronic payment method or a wallet where you can put funds in it and use it directly under their platform . so with that , i dont think they will have a reason to built a crypto based coin .
They isn't doing that because they hate crypto. It's just that 98% of everything being advertised on their website was either a scam or misleading.
Remember that anyone can create an ICO/token for the sake of getting a few bucks. The whole crypto ecosystem is still shady as f*ck and they don't have the time/desire to check every single ad and ICO before accepting them.