That's great news; but beware the next appointment.
When I got the best HbA1c I'd ever got (5.8%) my GP and nurse said that was too low and I needed to increase the carbs and get it up a bit. Like a fool I didn't question that and have been trying to get back to the 5% club ever since.
Most GPs and practice nurses whilst very well intentioned freak out about low carbing although as you are so obviously seeing it is the best way to go. The reasons they are concerned is that the LAW is that higher fat and higher protein is bad; we know different and no-one has provided any clinical studies to show that higher fat and higher protein is a problem but there we are; it's THE LAW.
So, if there is a storm, weather it and make sure your dad keeps on doing what he's doing.
Best
Dillinger