Vet says my ragdoll is overweight?

We've just recently acquired a 4.5 year old ragdoll male and took him for his first check up.

He weighed in at 6.5kg, which I have read elsewhere is normal (with the range typically being 5 - 9 kg) and has said he needs to lose a full kg.

He doesn't particularly bulge, and when you run your hands firmly down his side can feel his ribs.

I'm just a little confused and don't want to be doing my kitty a disservice!