Whatever DD told you is wrong.
803.01 A - Obstacles to a Stance or Throwing Motion: With the exception of casual obstacles to a stance as described below, a player is not allowed to move any obstacle on the course. No relief is granted from park equipment (such as signs, trash cans, or picnic tables), which is considered to be part of the course. A player is allowed to request that other people remove themselves and/or their belongings from the player's stance or line of play.
So if it's not an obstacle to the stance as described in B, it cannot be moved.
To expand on that, 802.04 A is even more explicit on this:
A player must choose the stance that will result in the least movement of any part of any obstacle that is a permanent or integral part of the course. Once a legal stance is taken, the player may not move an obstacle in any way in order to make room for a throwing motion. It is legal for a player's throwing motion to cause incidental movement of an obstacle.