First line of the link says "There's a random value from 0-30 which represents the windstrength." According to the code it says "windStrength = 10 + Random.nextInt(10)" which is a value between 10-19.
So there is either more hidden mechanic that I wasn't able to find or your information is outdated.
Yeah that's the initial windStrength. Windstrength is constantly changing.
In onTickInGame you can see once every 128 ticks updateWind() is called:
public static void updateWind() {
int upChance = 10;
int downChance = 10;
if (windStrength > 20) {
upChance -= windStrength - 20;
}
if (windStrength < 10) {
downChance -= 10 - windStrength;
}
if (random.nextInt(100) <= upChance) {
windStrength += 1;
return;
}
if (random.nextInt(100) <= downChance) {
windStrength -= 1;
return;
}
}
When wind = 30, upchance = 0 and it can only go down, when wind = 0, downchance = 0 and it can only go up.