Good question. There are three main differences:
1) Metafact is based on people asking binary questions (ie True/false) not open-ended questions like most of the questions on Quora.
2) Metafact only publishes answers from verified experts who have credentials and knowledge on the question. On Quora, anyone can answer any question.
3) We aggregate answers to form a consensus score or rating based on many independent experts.
We see Metafact as a good compliment to both Wikipedia and Quora - where when you really want to check a claim, answer or article - we provide the tools for you to check it.