Well at the time I wrote that not much was known. It was probably one person who did the acts, but it's still very possible (and likely, imo) that he is part of a larger group of activists with a shared cause.
They torched a bunch of police cars in PDX earlier this year, and before that several pieces of heavy equipment owned by the city. They call themselves the "Rachel Corrie's Ghost Brigade".
Pro-Palestinian activists that organize and meet at the local community college. PDX has a long history of this kind of activism, going back to before the WTO business in Seattle.
If they don't catch this guy, it will because he has moved to a different city. "They" also do that a lot.