MigMan
Start with a lacquer based primer; then preshade with an enamel paint; then you could lay down an acrylic base color.
The statement is basically correct in that it describes one way it could be done, but it doesn't have to be done that way. E.g. you can preshade with acrylic instead of enamel.
What you are referring to is called the LEA rule (Lacquer, Enamel, Acrylic). This describes what is supposedly the only way to layer different paint types. It fails to mention that you can also layer acrylic over acrylic. Personally, I don't use enamels, so this simplifies things for me.
The problem with the LEA rule is that there are many exceptions. For example, modelers often spray Testors Dullcote over acrylic paint. Since Dullcote is a lacquer, it would seem to violate the rule. But many modelers do it anyway, and will remind you to spray the dullcote in light coats and allow the acrylic paint to fully cure before you spray it.
Another area where the LEA rule fall apart is in brush painting. Lots of figure painters (myself included) brush paint enamls or oils over acrylic paint without problems. But those same figure painters will never paint an acrylic over oil paint. I've even brush painted a lacquer over acrylic, using a different technique.
Basically, if you follow the LEA rule when airbrushing, you won't go wrong. But you are also limiting yourself somewhat. If you are a beginner, following the LEA rule is a good idea. If you wish to 'violate' the rule, always test on scrap plastic or a spare model before you try it for real.