You main take a way should be that if your scale shows you getting too light or too heavy, then somethings got to change. Either the amount of Calories in, or the amount of Calories out.
I don't worry about five pounds (2.3kg) gain or loss between days. It's what is trending over months.
Your focus on foods you just ate being contributing factors to your issues might be misleading you.
Also, cycling is a cardio exercise. If you are needing to get some muscles then the gym is the better place for that.