I think that email was really positive and said quite a lot. He trusts that he can say things that may be a little emotive and feels safe to do so. Just carry on as your doing and he will feel safer and safer. It may be that he was clawing back a little control, but that's fine.
What you are doing is working and it is natural for our WAS to draw back a little once they have opened up. After all they have been so guarded for so long, it must be a hard habit to break and let go of.
