It is hard to argue with his accuracy. He has a source, and they nailed the 21st.Beta 3 is coming on July 10th according to the Reddit guy. This makes sense since it'll be two weeks since PB.
It is nice to have a source for once. It really wouldn't kill Apple to have a release schedule, even if it changes periodically. Would really help developers that run up against bugs preventing further development plan their schedule, and prevent public beta testers from jumping ship and downgrading. Doesn't do Apple any good to keep a tight lid on the beta release schedule.