Stopped going to gym for a month and came back stronger than before?

Im 16 years old. I stopped going to the gym for over a month. I went back yesterday, the first thing I noticed was that I was able to lift 70kg for 5 repetitions. Before I was unable to get past 65! Another thing is that I was drinking alcohol every weekend and not keeping a good diet. How is this possible? Could it have been strength from the months of workouts that hadnt kicked in yet? Or could it just be me my body developing?