The truck ahead of you signals a right turn but first moves toward the left side of its lane. What is most likely happening?

Why

Long vehicles cannot turn as tightly as cars, so they often need extra room to make a turn. For a right turn that means moving to the left first, which can look like the driver is heading the other way. The manual's advice is to watch the turn signals, because the signal tells you the real plan while the truck's position can mislead you. Taking the empty space on its right as an invitation to pass is the dangerous mistake here: that space closes as the truck turns, and the manual also warns you not to linger near a large vehicle in the wide area it needs to turn, where the driver may not see you. Believe the signal rather than the drift, because a truck easing left with its right signal on is setting up a right turn.