The only limit on the free choice of armor during character creation is the cultural standard of living.
You're right in that the use of the game term favoured doesn't make sense here. Neither cultures nor callings have anything to say about favoured armor.
In first edition it was your "chosen" armor/helm/shield. I suspect this was also the intention here, to give you free choice in your starting gear during character creation. This wouldn't be the first error introduced by, say, experimenting with language during editing passes and bit of lax oversight when favoured became purely a game term with the formatting to match.
However, you should also keep in mind that the initial loadout of weapons and armor is one of the prime determiners of a character's load, and the best starting armor is also the heaviest. A starting Barding adventurer can certainly head out on the road with a helm, great shield, and coat of mail! But add a stout blade to that and, even if they spend their starting rewards on easing their burden (cunning make/hardiness), they're only a couple of bad days on the road away from Weary, without even taking a single blow.