You quoted it yourself:
The Move action allows 1 troop to move.
It is not mandatory to move all the units of the troop; the player can leave some of them on his way. Furthermore, the player can gather units from spaces on his way, as long as he doesn’t exceed the movement capacity.
The difference in wording there is just a text inconsistency. The point the general rule makes is, you choose the size of the troop you want to move.