Not quite correct. Trading occurs on an exchange, and does not typically show up in the block chain immediately.
In the block you reference, one person sent 84k or 164k (you cannot know which is the change TX, sent back to one's self).
Two 10k chunks were then peeled off that 164k chunk.
570k is simply a dumb total of the BTC in the block, including all change transactions sent back to yourself. A "true" total would probably be closer to 200k, and even then, you cannot know if someone isn't simply sending change to another wallet of their own.
Background: Every time you sent bitcoins from person A to person B, let's say 100 BTC, bitcoin software finds a "coin" of at least 100 BTC. If it cannot find a coin of exactly 100 BTC in size, it takes a larger coin and splits the coin into two pieces. If person A only has a 1000 BTC coin, then
http://blockexplorer.com/ will show a transaction with two outputs: 100 BTC (spend) and 900 BTC (change). The latter 900 BTC is sent from yourself, to yourself.
