It's the probe rating. It'll be interesting to see how long the USB electronics survive if they get up to that temperature. Industrial temperature range is typically only up to 70C and I don't think I've ever seen even Automotive/Military IC's that can operate at 130C

What you're looking for is pretty easy to build at lower temperatures: just put a temperature probe in a stainless steel housing and route the sensor leads out to USB data collection that's at a safe temperature. The off the shelf units tend to be expensive because they're aimed at food-grade applications, not at hobbyists.

At temperatures of 550F, then you need to use thermocouples which are a bit harder to interface to, so hobbyists tend to shy away. Again, plenty of commercial products at this range, but expensive.