Answer:
I believe the sentence is an example of simile.
Step-by-step explanation:
A simile is a literary device which compares two different things. The purpose is to attribute the qualities of one to the other. In that sense, simile and metaphor are the same thing. What distinguishes them is that a simile will use the words "as" or "like" to establish the comparison, while the metaphor will not. For example, "your eyes are like stars" is a simile. On the other hand, "your eyes are stars" is a metaphor.
Thus, we can easily find the simile in the sentence we are analyzing here when the author says "he stood like a rock." He is comparing a person to a rock, probably with the purpose of saying that person stood there, unmoving - the same way a rock does not move.