This is a contentious topic on Medium. I think if someone agrees to a forum where reciprocal engagement is expected (such as Facebook groups and other avenues where there is a type of agreement), that it is good if you monitor how people engage when you have engaged with them. This is because you are putting in your time under an agreement.

However, general Medium reading, like if you come across an article on a topic you like that was recommended by Medium, I don't think that author "owes" you anything. If your feedback is voluntary I think it is nice if that is acknowledged but, again, not required.