I don't agree with what Sam Odio did initially, but I also wouldn't exactly call publishing a screenshot of a private email from someone the "high road".
There was no private content in that mail. The whole of it could be expressed as "LOL UMAD?". I don't think I would have responded so kindly in Jonathan's place. I probably would have taken this as an opportunity to tell Sam Odio what I really think of his actions. So, yes, compared to that Jonathan absolutely took the high road. But also from a philosophical perspective, redirecting this toward the public participants of the card experiment was absolutely the right thing to do.
I think it doesn't matter if there was private content or not.
The same way Sam violated the social contract of the experiment, I think Johnathan violated the social contract of email.
We all realize email we send could be read by anyone, but still don't want it copied and pasted in a public forum.
What Jonathan did is of course less annoying, but I still nevertheless find it of a similar nature. I think he could have still made the post and just paraphrased.