That is why it has been mentioned here only briefly without going into details. Also, there may be another explanation for it. Apparently the first announcement, I am going to make in the earth a vicegerent , had shown that the said vicegerent would have authority over the angels too. It may be inferred from the command obliging them to prostrate before Adam. Probably on hearing that first announcement some disturbing thought had come into their minds, as it had never occurred to them that any earthly creature could be given authority over everything including themselves.
Some traditions too point to it.
In this context the words, what you were hiding , could easily be addressed to the angels. The worshipper places himself in the position of servitude and performs what manifests this status, which clearly shows that he accepts the mastership of his master. The more apt an action is to show this status, the more reserved it becomes to the rites of the divine worship. Prostration is the most significant symbol of the master's status and the servant's low rank, because the man in this act falls down and puts his forehead on the ground. For this reason, it has the strongest connection with the divine worship.