Does eating in a lunch buffet help muscle gain?

Last year on March I went to InBody body composition analysis. 9 months later on December, I went to the same analysis to see the results. I kept my training regime the same as before the 1st analysis but I started to eat more by eating in the lunch buffet 3 times a week. Eating enough to gain mass has been a challange for me. The result was that I gained weight 2,5 KG. My muscle mass increased 0,6 KG and fat mass increased 1,7 KG. Which means that the rest of the difference was water. During the 9 month period I would have liked to have longer training sessions. I felt that it would be nice to train more. Basically I ate too much or I should have trained more in order to avoid gaining fat mass. My conclusion is that gaining muscle mass is tough.