Some of the men who were the “thieves” at the waters of Sebus are in the group of people called to the king’s chamber. This suggests that they were both near, and entitled to information about the king. In Mesoamerican terms, this places them among the elite in the society, and probably of a different lineage than the king.
The close proximity of men who had caused such disruption for the king suggests that they had to have been known, and that the king was required to tolerate their actions. Rather than simple thieves, they are probably a rival elite lineage, attempting to weaken the rule of the king. While there isn’t much information, and the only explicit information given is that of Mormon interjecting the idea that these Lamanites are thieves like any other, the rest of the text belies Mormon’s conclusion.
The fact that these men would be so soon called to the bedchamber of the king suggests that they were known. The servants who had been executed were only executed after their return, giving them ample time to identify their assailants. The only plausible situation which meets these requirements is a rival elite lineage that the king cannot censure for political reasons. As Mormon would be oblivious to those internal politics, he essentially makes up a reason.