I don't think anyone meant any offense.
For me, even though the therapist has mentioned ptsd and me, I actually would still write and send letters to the therapist even if they said no letters. It might make me feel panicky, dry mouthed and nauseous, but them telling me I could not would just be ridiculous to me. I would probably do letter rather than email (because I think there are all sorts of difficulties with email) - but their setting what seemed to me a stupid pointless rule would not cause me to blindly follow it. I do think there is a difference between the idea of plain rules versus boundaries in some places. (For me there have been times when the therapist has even been more than just not unhappy that I did openly not follow a rule.) A big problem for me with the example is that I really don't see being sent email as something that should send the therapist over the edge. Getting caught up in responding to email is where I see the difficulty and that is upon the therapist, as I explained earlier. But that is just my take on it.
I still don't think the labels are useful here. No matter what the label. But I would not see a therapist who had more than a "pay the agreed upon amount for the agreed upon amount of time and leave without shooting me" rule in the first place. I do like to know the rules ahead of time.
We all pick the rules we are going to follow or not - for example - traffic laws: speeding (even just a little over the speed limit), rolling through a stop sign, not wearing a seat belt (I never wear them) and so forth.