Always good to get back into it! I read a quote from an Okinawan Karate Master (may even have been on the FA website!) and it was something like "It does not matter how long something takes you, as long as you keep going!"
Anyone who has trained for any amount of time will have missed training for a decent stretch at some point. Little thing called everyday life tends to get in the way now and again for a lot of us lol!
Regarding you picking it up again so easily... your mind is an extraordinary piece of engineering. When you concsiously learn something, it goes into your subconscious mind. All the while, though you are not aware of it, your subconscious mind is swishing it around and working on what you have learned.
Have you ever looked a particular problem, say a maths problem, that you couldn't figure out? You look at if forever, and nothing comes of it. You get up and go do watch some TV for an hour, come back to it, and 10 minutes later you have the answer!!!
Your subconscious mind was processing the information you conscious mind had taken in. It was working on it the whole time.
It may very well be that although you weren't at class, your mind was still working on what you had learned, so it was easier to remember.
"Let your food be your medicine, and your medicine be your food"