Yeah the airtrain platform on the far side should take you non stop to T7, the platform nearest the terminal building goes the other (wrong) way in this context. The signs can be very unclear and only update a few seconds before the incoming airtrain comes through on the screens above the relevant doors. It is confusing. I know it was working that evening since I had a similar issue (photos included):

http://www.flyertalk.com/forum/briti...eb-2016-a.html

I was on Iberia's MAD to JFK T7, and we had a very difficult landing, 2 turnarounds, long hold over Fire Island (over an hour) and the runway closed behind us when we did land. The captain said the situation was "marginal" and the two alternatives for me were PHL and indeed Hartford. I used the IB wifi to check that the trains were working from Hartford, which they were, as well as PHL, so my connection was going to be OK. So in your shoes I'd have got off at Hartford, rather than risking an overnight there.