Witnessing an accident?

[RepSpec]

driving along today i pulled out onto the highway near my work behind a ute and a truck.
i went into the right lane behind the ute and noticed it was in good nick... look around at the scenary and then look up and see the ute has his lights on and stuff flying everywhere. from the looks of it the tuck for some reason has turned into his lane and taken out the rear bumper and light (XF ute).

i saw them pull over up ahead and got out and were talking.

my question, should i have stopped even though i only half saw what happened.

after thinking about it now and looking back, the truck i believe would have been in the wrong and cut into the lane too quickly to avoid himself having an accident in his own lane because he was following too close to someone else.