It seems like "humanism" may have been an auto-correct? In any case, Klingonists do believe that Okrand had in mind Ysengrimus when this word came about, but it means something else in Klingon and is not intended to be a direct reference.
"Humanism" was my word. By that I mean an English word that Klingon Hol borrowed, and adapted for itself. But it's not, and what you described about the origin of the Klingonese word, is what I figured out.
"To behave as, to act in the manner of". It means that the subject is doing the same things that you would normally expect the object to do. So this sentence is telling you not to do the things that an 'I'SeghIm would do.