i feel like the translation is horribly wrong. That guy is stronger then the MC, the MC knows far more and is far more skilled in arrays and medicines. its obvious the old guy wants the MC alive because he wants her knowledge. if he wanted sax he would buy a prostitute. From the context alone its 100% clear he intends to keep her as a slave to either work for him directly, to teach him or to act as a library of knowledge. its either the author misunderstanding the term and or the TL not understanding one of its meanings.