This is VERY doubtful. You did not lose muscle in 4-6 weeks. Not if you kept training hard and eating enough protein and were not under 10% body fat.+
You don’t easily lose muscle when you keep training. It’s the last strategy the body will use to accomodate to a lowered caloric intake. It will use several other ones prior to that. Muscle is useful, especially if you keep using it by lifting. The body doesn’t really want to part with it, especially not if there are other options available.
When you are in a caloric deficit the body will start by increasing hunger. This is a strategy to try to get you to eat more calories. At this point it’s fairly easy to stay disciplined and not jump off of the dieting bandwagon.
If that doesn’t work (you are still in a deficit) the body will subconsciouly try to decrease how much fuel you are burning daily… you will become a bit lazier… you won’t move as much, fidget less,etc. Oftentimes it’s not even noticeable. And if you keep training hard, chances are that it won’t be enough to stop being in a deficit.
Then the body will try to decrease metabolic rate by reducing T4 to T3 conversion. By decrease metabolic rate you can lower how much calories you are burning significantly. It’s like turning down the heating in your house by a few degrees: you will be using a lot less electricity. This is where you might start to feel cold and fat loss slows down.
If that’s not enough you will start to have much bigger cravings. Your body is trying to force you to eat caloric dense food by having your hormones and neurotransmitters act on your brain and body. It will not be a lot harder to resist the urge to eat crap.
But if you manageto stay the course NOW the body might consider dropping muscle to reduce energy expenditure.
Most people who train hard to not reach that stage until they have lost A LOT of fat.
So NO, unless you did something stupid like consuming 600 calories a day and almost no protein, you didn’t lose musce.
What likely happened is that you got flat. When you reduce calories (and likely carbs) you decrease muscle glycogen stores (carbs stored in the muscles). A 220lbs man can likely store 400g of carbs in his muscles. And each gram is stored with 3g of water for a total of 1.6kg or 3.5bs. When you cut calories and carbs a good portion of that is lost. You could have easily lost 2 -2.5lbs of glycogen/water. But since it was stored in the muscle, it looks and feels like you lost muscle.
The change in intramuscular pressure/leverage also decrease strength a bit, which can reinforce the belief that you lost muscle.
On top of that if you carry a significant amount of fat (more than 15%,which you likely are even though most weight training men believe that they are 12% or so when they really are 18% or so) losing 10 or so pounds will not make you look better. You won’t be lean enough to see a real difference, but you will feel smaller in your clothers, also making you believe that since you don’t look leaner, but are smaller, you lost muscle.
The fact is that most people don’t diet down long enough to reach a level of leaness that makes them look better.