Scuba Diver Out of Air and Emergency Ascent - Catastrophic Buddy failure

Scuba Diver Out of Air and Emergency Ascent - Catastrophic Buddy failure
This event was sent to me by Louise R, an out of air emergency from 2017. Two divers on a working dive, one runs low on air and cannot communicate this to the more experienced diver. Shortly after this miscommunication, the diver runs out of air totally, loses his buoyancy and is unable to reach the unaware buddy for an air share. The only option left for this out of air diver is an emergency ascent to the surface (from 13m), which he does successfully with no lasting injuries or effects.

Original video:
https://www.youtube.com/watch?v=43LHQN3ijrw
Background information from the original video description:
The water temperature was 3C / 37.4F, this was during winter and in salt water. The diver shown in the video was in a sidemount configuration with two 12 liter / 85 cuft tanks while his buddy who ran out of gas used a single 12 liter / 75 cuft tank (85cf?). The purpose of the dive was underwater work, more specifically running a line from shore to several underwater items that were marked for removal. The diver who took the video did not participate in the work portion but tagged along to take video. The average depth was around 13.5 m / 44 ft and the total dive time just over 50 minutes. Gas mismanagement by the OOA diver was the leading cause of the accident. He simply breathed his single tank dry. The attempt to signal the upcoming OOA is shown in the video, the actual signs are not visible. After getting his buddy's attention by grabbing the fins, the OOA diver moved a hand to touch his neck seal. After a delay, he touched his second stage regulator. All movements were extremely slow and as a result, the buddy thought the diver was just cold, plus maybe re-seating the second stage in his mouth. He clearly did not understand and made that very clear. While the communication between the two divers was going on (and failing), the diver ran out of gas. Losing his buoyancy and being abov..