As you're no doubt aware, Mr. Irony, menswear in this instance refers to a style of clothing that is more masculine and tailored than more of the frilly frou frou things they expect women to wear. "Menswear-inspired" might be a better choice. It's a look this season, as evidenced by all the tweed and houndstooth and tailoring. But you're right. It is silly to call pink pyjamas menswear.