Fitbit calories

Joramaisi3

So I track my food using MFP. I eat my given calories and what I burned. I never eat back what my Fitbit says I burned just with steps as it’s always so much. Well I decided to experiment and eat some back and I gained a pound this week when I’ve been losing, slowly but losing. How are people eating back all of their fitbit calories and still losing? Also I went for a 1 hour and 40 minute walk with a friend and we walking to the point where we were struggling to talk a bit. And Fitbit said I burned 1042 calories. That seems like a lot. My feet do hurt though:)