That's a good question. It was written and anonymous, and whoever it was never manifested themself again. And with the people from that time disappearing over the last two years...

[Chances are they'll never discover who it was.]

Team Rocket is a local criminal group. They've been known to attack important landmarks, trainers... and they are also known to have arrivals from other worlds within their ranks. Not that those arrivals necessarily chose to join them.