Honestly, don’t trust what Bing Chat says. You cannot determine if this is true or false.
These models are capable of telling very pertinent things or pure bullshit, just the same way.
I like to call them “Digital Politicians”.
Concerning Color LUTS with negative values : I’ve indeed encountered a few, and I think the real case of having negative values is to model “darker than dark” or “lighter than light” values, meaning saturated values with over- or -under luminance.
While this may be useful in a few cases, it’s generally not desirable if you just want to map colors on an input sRGB image.
Also, most of those LUTs appeared to be synthetically generated, and those negative values appeared more as just errors due to bad generation code :).