It was not just those. Boeing and a bunch of others had put options placed. See 2001 FR thread on it. Yes, there were people who knew that it would happen. At the time, it looked to me like they decided to cash in. Unfortunately for a lot of their plans, the US trading system was shut down for a while after 9/11, and the patterns were discovered before trading resumed
What surprisd me was how they (whoever they are) thought it even possible to make such trades and not have the spotlight shined on them. In case you haven't done so keyword 'WTC7 collapse' and you'll find video showing how fast (and symmetrical) it came down.