An interview with someone with a limited vocabulary who therefore does not understand the questions being asked is likely to produce

   Random error

Explanation:  Random error during the interview, which results from the limited vocabulary and misunderstanding of the questions, does not affect the general validity of the information obtained in the interview, i.e. during some survey. They do not affect the validity of the data because such errors are not systematic as a result of bias or other aspirations of the interviewers, and therefore, such random errors are unrelated to each other as far as meaning is concerned, that is, they exclude one another.

Systematic errors are those that are repeated several times as similar during the interview, i.e. interviewers constantly repeat similar mistakes, because they are tendentious and the tendency is to achieve some bias in the final research data.

chavez's example shows that nonviolent protest can work well. it shows that one nonviolent man can stop a mob, which proves chavez's point and persuades people to protest nonviolently.