Not feeling hungry. Make him eat faster?

My 4.5 yrs old son has no interest in eating food. Whenevr i feed him,he keep it in his mouth for long time and i need to remind constantly to chew the food. To avoid this, i started giving him mashed food but of no use. i dont think, he has chewing problem, because he eats other things fast and to our surprise at restaurants he is very quick in eating even tandoori roti. One day, i did not gave him food, and surprisingly he did not demanded, and on asking said, he is not hungry. On holidays, he did not demand food or say that he is hungry. But,yes, Maggi is his all time favourite which i permit him to eat only once in a week. What can be the problem, how should i make him eat faster? He recently had his tongue tie surgery but as i told, he eats other stuff easily and quickly...pls suggest some way to make him eat with some interest... At school, his teacher says that he eats easily without any delay but i am still unable to believe them.