The packets generally have a lot of salt and artificial flavourings like msg as well sometines, though this is getting less common - you need to consider the volume of salt going in in comparison to the volume of food. The baby in the story was very young, as your child grows, their tolerance to salt etc grows. I know what you mean about the convenience factor, but you need to remember that stock cubes etc are more or less pure salt, so that most people who say they don't use salt, actually do, it is just more hidden. It is all about proportion, If you are making a big batch of bolognaise and using one packet instead of stock, it is more or less the same thing. When you take it in proportion to the amount of food you are making and the amount the baby will be eating.
What you need to be wary of is processed foods like tinned soups as these are really high in salt, but home made soup with a bit of potato mashed in it to thicken it is a good meal.
Bread has salt in it along with pretty much everything we eat.
Enjoy your baby and give him what you eat, just be a wee bit careful and sensible