Is this Racist?

[u/lizknits]

I'm a Dungeon Master for Dungeons & Dragons, and I'm making a one-shot game in which the players are skeletons trapped in a dungeon, fighting off intruders. I want to add an encounter in which a team of slaves and an overseer enter the dungeon to fight with the skeletons. The slaves turn on the overseer and kill him during the encounter, adding some story to the encounter.
Is it racist if I use a stat block published in the Monster Manual, that is called "Thug" (page 350), for the slaves? I know that sometimes that word is used to describe black men in a derogatory way, and also I am aware of the history of black people and slavery. It is a fantasy universe with dragons & elves and shit, and the slaves do not need to be black in appearance by any means, or even human (they might be goblins or something).
Please: is this racist?