Even so, normally, you only see the socks peeking out between the shoes and the pants when the person sits or kneels, and otherwise you see pants and shoes only. So to see shoes and then a long stretch of socks would look odd to me, like you were wearing stockings or capris (both girls clothes). Furthermore, most cassocks I’ve seen come well above the ankles when the person wearing them is sitting. I wouldn’t be surprised to see the top of your socks and your legs above them in such a case. Of course, I’ll take you at your word that nothing was visible, but jeans would just make more sense and raise no questions or curiosity. I’m certainly no expert in what is supposed to be worn under the cassock by the laity, but I would say that when you are in a pinch again, and you have to make the best out of 2 less than ideal choices, casual clothes are better than faking clothes.