I cannot answer the question, but can probably provide some info that may assist your quest.
I have experience skydiving (several hundred jumps) and soaring (several hundred hours).
One thing you should know about soaring, pilots deliberately seek out developing thunderheads. This may sound screwy, but is easily explainable. In the desert Southwest (at least), thunderheads develop in isolation. What these isolated clouds are marking is a very strong thermal. These are sought out while they are developing and before rain is coming from them. It is prudent to exit the thermal before you get too close to the bottom of the cloud. Mistakes here have gotten more than a couple pilots in trouble. Sailplane pilots frequently wear parachutes as well. All this makes the idea of several pilots finding themselves in a really bad spot and deciding to bail out pretty reasonable.
As a skydiver, I can tell you that people do survive falls without their parachute. This isn’t exactly common, but not unheard of. I can’t think of a documented case of anyone “walking away” from a fall without an open parachute. Many of the no parachute stories are really without ANY parachute. Typically, the person has at least something out increasing drag and reducing impact speed. Good? No. But better than nothing.
What would make more sense is this.
*Pilots get into trouble in an intense thunderstorm.
*Pilots bail out.
*Pilots are held in the thunderhead by the intense updraft and to come degree covered in ice.
*Pilots eventually fall out of cloud.
*One of the pilots has little enough ice on him, is still conscious, etc… and manages to use his parachute and survives.
Did the story say he didn’t have a parachute?
Did the story say he survived without injury, or just survived?