Rametto and Sherco40 thank you for discovering those two custom road categories!!!
Those two are not routable and in reality the "thin road 0x10805" is most of the times (where I've checked with streetview) not allowed for vehicles and the "thin trail 0x1080c" accessible only on foot.
They are drawn on map (default TYP) exactly the same as residential street and trail, exactly the same as the the two routable categories that Garmin uses in the cities.
So with the default TYP you can easily get crazy if you try to navigate these streets and you may came to believe that the map is wrong or the device is malfunctioning!!!