I've thrown people in the spam filter for a lot less. "re: twitter" as a subject line is even more objectionable to my personal tastes -- but I dislike journalists who are intentionally trying to mislead their audience, even in an email subject.
Confused as to why there is any objection to this. He stated that it'll typically get a reply that includes their email, and he is simply creating context within the subject line – this advantageous for the receiver.
If it were me (and I had indeed shared my email to the person reaching out on Twitter) I'd appreciate the reminder of how/why they are reaching out on email.