materials have different emissivity. Plastic on wire is ~1, metals are way different.

Metals also reflect heat from different sources. You can tell if you're measuring a reflection by moving yourself around and measuring from different angles. reflections will change but the emited ir wont

You need to put a bit of black insulation tape on the metal and use that for temperature. Or use it to work out the emissivity of the metal.

Theres another setting for specular reflectance. You crumple up some tinfoil and take a reading from that for background reflectance