He doesnt look fat and as someone else pointed out, his weight is very normal for his age.
My bub is actually around 12 kg now and he is only 8 months old! He too isn't fat, he is just really tall. And as you say, he is eating a healthy diet. Kids shouldnt be on a calorie restrictive diet.

Also I think there is a difference between saying a bub is big and saying he is fat. Having a big healthy baby is something to be proud of and I am sure that is all they mean to say.