No, charges under Article 93 of the UCMJ are not strictly limited to acts against a direct subordinate in one’s chain of command. The text of the article states that it applies to any service member who is “cruel toward, or oppresses or maltreats any person subject to his orders.” The key phrase is “subject to his orders,” which is interpreted more broadly than just direct subordinates.
This means that an NCO or officer can be charged with maltreatment for abusing any service member over whom they have a position of authority at that moment, even if that person is not in their formal rating chain. For example, an NCO serving as an instructor at a military school has authority over all the students, and they can be charged under Article 93 for mistreating any of them. Similarly, a staff NCO in charge of a detail has authority over all the junior soldiers assigned to that detail.
A military attorney analyzing an Article 93 charge will first examine this element of the offense. They will determine if the accused individual actually had the requisite position of authority over the alleged victim at the time of the incident. If the accused and the victim were peers with no command or supervisory relationship, then Article 93 would not apply. The misconduct might be chargeable as an assault under Article 128, but it would not be the specific offense of cruelty and maltreatment.