Ah, so "The Poker Leaderboard" export, which is now a defunct site. I've actually removed that export from the latest version.
That is apparently the default way to represent boolean for XML. 0 for false and -1 for true. For other exports, such as StatsGenie, the TD code actually sets the value to 0 or 1, whereas this export sets the value to an actual boolean (true/false), and the internal XML code (internal to Internet Explorer) translates that to -1/0. I don't recall a reason why one export would be different from another in this regard. It is likely I coded the StatsGenie export differently as I probably had actual specifications to use from the StatsGenie staff. I am still in contact with Martin from SG and still make changes when necessary.
By the way, there actually is code to export to JSON, but it's not exposed. I think it had an eventual purpose that never panned out, so it was never completed (there's plenty of stuff missing as well as plenty of stuff that is unnecessary). If you could get to it, you would see that it is actually broken in the latest version. There's a bug but I didn't even know it existed because there's no way to trigger a JSON export. I think in the next big version I will break out the "TD" export into HTML/XML/JSON options.