This is not a normal highway, The Natchez Trace is a recreational road and scenic drive through. The double yellow lines mean no passing. The truck that passed first in the video, did so illegally, but did at least change to the other lane. Riding single file give drives the wrong idea that they can pass and not cross the double yellow line, which they seem to think they can do a lot of the time. When riding two abreast, they are letting the drivers know that they are owning the lane for their safety.

They are not impeding the normal flow of traffic and almost all cyclists will pull out when the road conditions allow, for the drivers to pass.

This was not a safe place for the drivers to pass and it is reasonable for the cyclists to own the lane. Tennessee law allows for this.

https://www.tn.gov/tdot/article/bikeped-bikelaws

TCA 55-8-175 - Riding on Roadways and Bike Paths – Penalty

(a) (1) Any person operating a bicycle upon a roadway at less than the normal speed of traffic at the time and place and under the conditions then existing shall ride as close as practicable to the right-hand curb or edge of the roadway, except under any of the following situations: (A) When overtaking and passing another vehicle proceeding in the same direction; (B) When preparing for a left turn at an intersection or into a private road or driveway; or (C) When reasonably necessary to avoid conditions including, but not limited to, fixed or moving objects, parked or moving vehicles, pedestrians, animals, surface hazards, or substandard width lanes that make it unsafe to continue along the right-hand curb or edge. For purposes of this section, "substandard width lane" means a lane that is too narrow for a bicycle and another vehicle to travel safely side by side within the lane. (2) This subsection (a) does not apply to a certified police cyclist engaged in the lawful performance of duty relating to traffic control. (b)

(1) Persons riding bicycles upon a roadway shall not ride more than two (2) abreast except on paths or parts of roadways set aside for the exclusive use of bicycles. Persons riding two (2) abreast shall not impede the normal and reasonable movement of traffic and, on a laned roadway, shall ride within a single lane. (2) Subdivision (b)(1) does not apply to a certified police cyclist engaged in the lawful performance of duty relating to traffic control or in pursuit of an actual or suspected violator of the law. (c) (1) This subsection (c) shall be known and may be cited as the "Jeff Roth and Brian Brown Bicycle Protection Act of 2007." (2) The operator of a motor vehicle, when overtaking and passing a bicycle proceeding in the same direction on the roadway, shall leave a safe distance between the motor vehicle and the bicycle of not less than three feet (3') and shall maintain the clearance until safely past the overtaken bicycle. (d) A violation of this section is a Class C misdemeanor.