Sealed, long, thin glass tube with two wires and tiny filament - what is this?
I'm thinking more like RTD. With a thermocouple, the two leads would be two different materials. With an RTD, the very thin wire at the tip would be platinum, and its resistance would change in a calibrated way with temperature.

Can you put it under a microscope of some sort? I bet you'll find that there's a very tiny coil of the very fine wire embedded in the glass at the very tip.