The evolution of the word reflects its historical use. While "caldarium" referred to a bathhouse, "chaudron" eventually shifted to mean a large pot or kettle used for cooking or boiling. This makes sense since cauldrons were often used over fire, much like a hot bath would have been in ancient times.
Over time, the word "chaudron" made its way into English as "cauldron," retaining its meaning of a large cooking pot.