Whether or not there was any explicit information in the plates we do not know, but Mormon understands that this increase in hostility is not a governmentally sanctioned effort. These are apparently individuals who are pushing the limits of their treaty. They appear to want to fall upon the Limhites to slay them, but restrain themselves because of the oath.
The result is that the desire to harm is displayed in individual situations (slapping and overburdening) rather than military situations. The original plate source could have understood this implicitly, but it is not likely that there was an official recognition by the Lamanites of the type of harassment that was being applied. Therefore, either Mormon is interpreting the situation based on what he read, or the plate source did the interpreting, and Mormon is echoing it.
Given those two options, I would favor Mormon as the interpreter. The actions of the Limhites appear to suggest that they did not fully understand the nature of the attacks upon them, which will result in their military response.