I'll admit, I'm painting in broad strokes here, but, let's be fair: lots of people judge magazines like Cosmopolitan because it is tailored to a particular gender. Not everyone, yes -- but lots and lots and lots, to the point where it's almost meme-worthy to say "this is good advice ... but it came from Cosmo, so take it with a grain of salt."
Regarding the article you cited to? The veracity of the advice depends entirely on the reader and the subject. Yet the thrust of the article is, if your guy becomes secretive, changes his habits completely, or offers really detailed explanations where he didn't before, he may be hiding something ... and that something might be cheating. This isn't bad advice, but it's not 100 percent accurate -- nor should it be considered so.
If Cosmopolitan is to be judged on its basic (I mean this in a derogatory way) relationship advice, then go ahead and judge the advice so. But if you're going to go out and say "well, that sounds like great words to live by, but since it came from Cosmo, maybe not so much, ha ha", that rings in my head -- and maybe mine alone -- like saying "well, that sounds like a great investment advice, Becky, but since it came from you, a woman, I think I'll go with what Jim Cramer has to say, ha ha."
I don't mean to say that ThatGuyThere went that far, but I'm stepping in to say, hey, let's not disregard something or treat it as lesser simply because it comes from Cosmo.