I think we can't know until the report comes out. Personally I think they aimed for the pillar thinking it would stop the vessel and cause less damage. There were cars and people on the bridge and if they hit that they knew they would have taken that part of the bridge apart and not stopped likely killing everyone on there at the time and definitely destroying the bridge before continuing on out of control and without power.
I don't think they thought for one minute if they hit where they did that the entire bridge would have collapsed. If I was at the helm I would have done exactly the same (if it was intentional) and of course, that's just my opinion of what happened.