[Goldeye]

Originally Posted by Section 7.2.1

POSSESSION: a GAME PIECE is considered to be in the POSSESSION of a ROBOT if it is being fully supported by the ROBOT, or if the ROBOT is controlling the position and movement of the GAME PIECE. A GAME PIECE on the floor is considered to be in the POSSESSION of a ROBOT if it contacts the ROBOT at more than a single point (e.g. the ROBOT has a concave "plow" feature that is used to push the GAME PIECE in a controlled manner)

The bolded part seems to hint a distinction for tubes on the ground.
Furthermore, although it is illegal to grab a tube that is in another team's possession, it would most certainly be alright for bluabot to grab the tube on the left while redabot is pushing it through a series of tubes.