in FACT is,
You have just quoted a small section of the section on setting the command speed bug. You need to go back to the top of the section titled "Landing" & read the lot again - carefully.
To simplify -
*When using autothrottle to touchdown set the command speed bug to Vref +5.
*When planning to disconnect the autothrottle at any stage prior to touchdown, set the command speed bug as per the following -
1. Add 1/2 the steady headwind component + all of the gust to Vref (maximum Vref +20) & set that speed.
2. The minimum speed to be set on the command speed bug is Vref +5
3. The maximum speed to be set on the command speed bug is Vref +20
4. The steady headwind additive should be bleed off just prior to touchdown.
5. The gust additive should be maintained to touchdown
Examples -
1. Vref 120kts, Runway 18, wind 180/10. Bug set at 125, touchdown at 125
2. Vref 120kts, Rwy 18, wind 180/20G30. Bug set at 140 (steady headwind = 20, 1/2 of 20 = 10. Gust = 10, so 10 + 10 = additive 20), touchdown at 130 (bleed off the steady headwind additive of 10kts & just carry the gust additive of 10kts to touchdown).
There are examples given in the table above the section of the FCTM that you quoted.
In a lot of situations you will be touching down below the bugged speed. This is normal. However, you shouldn't be touching down below Vref +5. You also shouldn't be flying an approach above the bugged speed or touching down above Vref + the gust additive.
Hope that helps.