Exactly. He named a couple solo wingnuts from the right, but it is the left wing terrorists that are organising these attacks thru websites and loosely-knit cells.
Anybody who thinks about it rationally for 30 seconds realizes that it's a lot tougher to track a lone nutjob than the idiots who get together for regular planning sessions.
It took a long time to catch the unibomber because he was a lone nut job. A left winger in that case.