Hi Guang, you are absolutely right asking about the descriptions. There used to be much more sites with ODP descriptions. Today I have no good idea when the ODP description is used and why. Generally ATW has changed very much to using Google style snippets. Google style snippets are truly one of the worst things about Google serps, so I don't really understand why ATW has gone that route.
Like all search engines ATW crawls the ODP and follows the links. ODP listings carry a lot of weight for ATW ranking.