It's true that the rules could do with a refresh and it's something on our radar, but I want to be clear that we aren't permanently banning accounts where it appears that there's a consensual informal agreement between friends to share accounts for low impact activities.
and
We don't proactively look for accounts being shared locally between friends
Common sense clearly sides with him saying account sharing is fine. Also while he no longer works for Jagex he was under their employ when he commented this. At the very least it sheds real doubt on Jagex's stance on this and as such should be allowed as this post merely brings discussion about whether it's actually against the rules or not.