Not how the level-scaling works. 

 "For example, if a player clears out a dungeon at level 1, the enemies would be skeletons. If the player returns at level 4 or above, it could be full of trolls. The enemies' weapons are also leveled along with the treasure the player can find in chests and on enemies' bodies."

For one thing, it's very rare and near impossible to find trolls at level four.Secondly, trolls would never ever replace skeletons because they are on completely different leveled lists.The only thing that would replace a skeleton is another skeleton or eventually, a lich.