People with ADHD experience find it more difficult to choose doing mundane tasks when a more stimulating option is present. Additionally, they are more likely to employ unhealthy coping strategies like avoidance when faced with a chore that is associated with negative emotions. This can cascade into a cycle of feeling like a failure for lack of motivation causing further demotivation. So the difficulty isn't in the task, but in choosing to sit with the task and the associated emotional.
My mistake, so they were agreeing that body doubling is for people with ADHD then. Otherwise a less-charitable interpretation would be that GP is saying that using a website to schedule a stranger to watch you do mundane tasks over Zoom —in 2025– is the same thing as human companionship in general, but that would be a kind of strange thing to volunteer online unprompted