I wondered the same thing and did a quick search. It seems that the term "1D fluid" here refers to the Luttinger fluid (https://en.wikipedia.org/wiki/Luttinger_

I wondered the same thing and did a quick search. It seems that the term "1D fluid" here refers to the Luttinger fluid (https://en.wikipedia.org/wiki/Luttinger_liquid https://en.wikipedia.org/wiki/Luttinger_liquid), which is a theoretical model.