If someone wrote about how taking a twenty minute walk in nature made them more productive, I don't think anyone would reply 'I swear every day I see a "new" fad targeted at fixing one's mood and every time they're doing so much mental gymnastics to not use the word "exercise."'

Who cares if they're doing exercise or not? The person who takes walks presumably knows it's a form of exercise. They're not talking about the other forms, they may not be able to do Crossfit or go skiing, and they might not feel confident expressing opinions about the entirety of all exercise, but they definitely know that walking works for them.