Thank you for reaching out with your question. A user should be notified of a reply to their comment without needing to watch the guide. It is helpful to mention the user (@username) to direct the reply to the user who initially posted.
If your users are not receiving notifications about the comments, I would recommend that you have them change their notification settings by editing their user profile.
A user who comments on a guide will need to also select the option to watch the guide after commenting on the step, if you are interested in receiving notifications about the guide in general and not just the step comment.
If you have any additional questions, please reach out to email@example.com.