Reading science papers (my field is biochem, YMMV for other disciplines) is a lot of work if you're not already expert in its very specific field and topic.
Paper authors try to be as succinct/brief as possible, and in my experience editors generally encourage this as well. There are incentives to do so.
In order to understand what that part of the paper means, you would need to actually read every reference, and maybe even their references, and maybe even go up pretty far up the reference tree. You might try and take a shortcut by reading recent or well-cited review papers on that specific subject. In order to take a shortcut from that, you might try and consult a handful of textbooks.
If you were an expert in the field, you probably wouldn't need to refer to the textbooks, and you might even know the rough ideas behind enough of the papers and might check only a few of the references to be sure.
Then beyond this, any variation from the afore-cited methods will usually be detailed within the paper, possibly in further sections or in figures or tables (and from what I can see, that seems to be generally the case in this paper).