Another possibility: David Lee is the leak. It may have been Ron Conway suggesting he attend to see what was going on. Even if he isn't the leak I tend to think David Lee was there simply to find out what was happening for SV Angel, not having intent to form agreements.

What's the connection between Arrington and Conway? Someone told Mike about the meeting (as he wrote, he wasn't invited). Then someone told Arrington about the content of the meeting (Mike wasn't there). Connect the dots.

It's possible that Ron Conway intended to blow it up from the beginning, including his own plant there. But as it always happens the shrapnel takes the unexpected course. Consider this a badly botched operation.

Keep in mind Michael Arrington said he talked to three different people who were at the meeting. It's possible David Lee was one of them. I have a hard time believing all Angels assembled were comfortable with the direction the meetings appeared to be taking. I think someone (possibly publicly defensive, and with a flamboyant writing style) had the bright idea to bring Angels together for mutually beneficial agreements to control market forces affecting them, but before things went very far things went public.

This comment is under-voted based on its probability.

"Never attribute to malice that which is adequately explained by stupidity."

I think the simplest explanation is that Conway either wasn't aware of the agenda or wasn't aware of the scope of it. That would explain his regret for Lee being there.