The calculation of TyG is ln (fasting blood sugar) x triglycerides/2). Many studies make the error of calculating it as (ln (FBS x TG))/2. The only online calculator I've found, I think, falls into the latter category, or has worse errors - I didn't go through it too rigorously, but I put in values beyond what human life can sustain and didn't get close to the cut-off for this paper's bottom risk tier.
If you look at studies/calculator using the latter calculation, it looks like this study looks at really, really severe diabetics.
If you compare with the appropriate calculation, though, they're looking at more run-of-the-mill "not optimally treated and obese" diabetics.
Hosseini 2017 did a paper analyzing a number of other TyG papers and calculating results under both calculation methodologies, for context.
Please also note that this paper does not state when the results were collected. Insulin resistance/hyperglycemia is a symptom of sepsis - if these labs were drawn on already-severe patients, it would be entirely unclear whether they reflect a cause or an effect (or, as is almost certainly the case, both!).