No, despite how I worded it, the thermocouple does not specifically require a built-in ignitor. It's just a device that detects heat and closes a valve if not present. And mechanical thermocouples are incredibly simple devices, just a strip of metal with two different layers that bend when heat is present and returns normal when absent. They have been around forever. Similar tech to fuses really.

The big tell is if you have to manually hold the valve open to ignite the gas, as it does take a few seconds for the thermocouple to register a change. If you open the valve and immediately smell gas, then it is likely that you do not have a thermocouple.