I’m sorry but it’s not. They are running a regression model. You don’t need to show me that you can write down the equation but it is common to at least show something like ANOVA or just in general a table that shows your model and the coefficient estimates. It might be buried somewhere because the tables aren’t rendered next to the text but I couldn’t find it.

I‘m not sure why we call this community science if I have to explain why I would like to see the mathematical model that justifies the core result of a paper.