I don't see negative Kelvin in the article. I do see Kelvins with a negative exponent, which is just a positive value that asymptotically approaches zero.
My mistake, I thought that notation implied negative numbers. Thank you.
I was saying that the temperature of the Universe in the far future will be about 0.000000000000000000000000000001 kelvin, if our current theories are correct. This is 10^(-30) kelvin.