Nope, HN's CSS accommodates smaller screen sizes [1]:

    /* mobile device */
    @media only screen
    and (min-width : 300px)
    and (max-width : 750px) {
      #hnmain { width: 100%; min-width: 0; }
      body { padding: 0; margin: 0; width: 100%; }
      td { height: inherit !important; }
      .title, .comment { font-size: inherit;  }
      span.pagetop { display: block; margin: 3px 5px; font-size: 12px; line-height: normal }

Not perfect by any means but at least there's an attempt.

[1] https://news.ycombinator.com/news.css