IF they were indeed tresspassing (and all reports indicate they are on the roadside) then the sheriff would have been all too happy to make some arrests. Since that has not happened, I would take it that there has been no tresspassing.
The guy was a stupid jerk to fire off rounds in that situation. No matter what, HE endangered everyone around him, the protestors as well as the Secret Service...
No, in the interest of accuracy, they were not trespessing.