The person saw some exploit with curl headers, which damaged their life. That's upsetting, even if the email is misdirected, because Daniel just provided the infrastructure, and did not cause the specific abuse. What is wrong is the threat to life.
The second thing that is wrong is to respond to the second email by doxxing the author to the public. The second email showed that the threat was likely not specific and immanent, but venting. A reasonable response would be to notify the police. Or to reveal this case to the public explaining why this is misdirected, but without the author's name.