Can rhabdomyolysis happen to sedentary people when they suddenly do exercises that are considered light by athletic people?

Yes : This is famous, do not let it discourage you from returning to fitness. Ease into it, stay hydrated. Your physician can help

Rhabdomyolysis.: For rhabdomyolysis to occur, activity have to be severe enough to cause either significant inflammation or tearing of muscle fibers. This would not generally happen with “light“ activity, regardless of whether someone is athletic or not. I understand though, athletic people may tolerate more extremes of activity than others. But light activity should not cause rhabdomyolysis.