The first steps before flying start with learning the gear and going over the procedures (Source).
Then you start what is known as kiting or ground handling where the you get the wing up into the air and use the controls to steer it and learn how to handle it while staying on the ground.
True mastery of the sport starts with learning to control the wing on the ground. Unlike with a rigid wing aircraft, before we can begin to even think about taking off, our wing must first be “built” and placed overhead in just the right position. While many aspects of flying might come natural to new pilots, kiting is a skill that has no real comparison to anything we learn at a young age (even flying a regular kite). So new muscle memories must be developed from the ground up.
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These are the ground handling exercises that you will dive into right away:
- Gear inspection, prep and layout
- Pre-inflation body position
- Forward inflation
- Light wind “taxiing”
- Reverse wall building
- Reverse inflation
- Reverse kiting
- Forward kiting
- Wing shut down
- Emergency procedures
Source
Groundhandling can be trained anywhere when wind blows, short grass and almost flat is preferred terrain. Ideal wind strength is 4-6 m/s without gusts. With less wind, front launch should be trained, despite its use at thermic take off places is limited, few times a year you will need it. If there are obstacles between you and wind, wind gets broken and good only for advanced training. I found it good to train groundhandling all the time wind was good. Even for 10 minutes before or after soaring/flying. All the actions should be trained to level, where you do not think about an action required, but act correctly without thinking.
Source
Most paragliding is done by taking off from hills, but kiting/ground handling can be done on a flat soccer field (I have seen it done many times). These exercises teach the skills needed while the trainee is still on the ground.
As far as exercises go, there are a lot of times when the pilots hands are up high pulling down as that is how the paraglider is steered.
From what I can find, upper body strength does matter,
It's beneficial to have good upper body strength while flying your wing. The more you fly and handle your wing, the stronger the muscles in your arms will become. This increases and improves overall flexibility, mobility and range of motion.
Source
but it is also about technique.
Paragliding is about finesse and serenity, not strength and adrenaline. We work to build your skills and knowledge, in order to help you exercise good judgment as a pilot.
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To address your questions of whether the situation described is plausible, consider that paragliders get stuck in trees all the time.
STATE emergency service volunteers have helped to rescue a paraglider who stranded himself eight metres up a tree in the Gold Coast Hinterland.
Source
Also, while rare, paragliders have gotten high enough to pass out from lack of oxygen.
Ewa Wisnerska, 35, was sucked 32,000 ft into the air — so high that she lost consciousness from lack of oxygen and ice formed over her body. Hospital staff say the paraglider suffered severe frostbite from which she almost lost her ears.
The adventurer said it was a miracle that she survived: "You can't imagine the power. You feel like nothing, like a leaf from a tree going up," she said. "I can't do anything. It's raining and hailing and I'm still climbing — I'm lost."
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She regained consciousness mid-air about one hour later. "I wanted to fly around the clouds but I got sucked up 20 metres (67ft) per second into it and spiralled," she told The Sydney Morning Herald.
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Her ordeal was recorded by a global positioning beacon and a radio attached to her equipment. The swirling clouds released Miss Wisnerska from their grasp and she landed safely 40 miles from her launch, suffering frostbite to her face and with ice inside her lightweight flying suit — but otherwise unharmed.
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