What does it mean when a truck driver blinks the truck's lights after you pass?

• You should immediately slow down.
• The truck wants to race with you.
• You are cleared to pull back in front of the truck.
  Explanation:

  "If the driver blinks the truck’s lights after you pass, it’s a signal that you are cleared to pull back in front of the truck. Move back only when you can see the front of the truck in your rearview mirror."
• The truck is having mechanical issues.