Well, I'm fairly noob to be able to answer any question, but from my understanding is that every muscle requires some form of maintenance/upkeep. That would explain why people in comas lose a lot of muscle and strength. So in a way, yes?
There are a few principles which can be applied to all forms of physical training. One of them is the princeple of disuse. When you stop working out you will loose your gains and your fitness will decrease to a level which is only needed for daily demands.
Unless you starve yourself you won't loose all the gains. You will loose some,but not completely. I still have some of my "swimmer lats" since I was 18,and I only started working out two years ago ...and my lats never disappeared.
Bingo. Although a noob could put on a solid 8+ lbs of lean mass in a month with proper diet, there could also be no real gains at all with inadequate diet. A week off is not enough time to lose gains. And as fireplug said, sometimes it's exactly what you need to come back bigger and sronger.
From seeing pictures of real young Ronnie and him carrying around 275+ lbs of lean body mass it seems impossible with his genetics he'd ever be "normal" unless he stopped training, had heart surgery, and was governor of California maybe
You didnt lose muscle, just some of the water/glycogen i would guess, and the swelling from all that overtraining damage you were probably doing!
I expect you wouldnt have gained much actual muscle in month of arm specialisation.
Anyway, dont worry.
You keep gained muscle a long time but it will dwindle if you dont train or if you eat too little - you dont have to train as hard to keep it as to get it by all accounts but train you should. If you dont enjoy the journey you dont get to stay at the destination!