Fancybox disable preload option does not work?

As I understand it, the “preload” in Fancybox means when I click open slide 2, it will automatically download and load slide 1 and slide 3, such that when I switch to prev or next slide, there will be no loading time. But either set preload to be true or false, I see that when I open one slide, the next slide is still fetched. Not sure if I set something incorrectly

<a data-fancybox="gallery" href="https://sample-videos.com/img/Sample-jpg-image-100kb.jpg" data-type="iframe" data-preload="false">
            <img src="https://sample-videos.com/img/Sample-jpg-image-50kb.jpg">
</a>
<a data-fancybox="gallery" href="https://sample-videos.com/img/Sample-png-image-200kb.png" data-type="iframe" data-preload="false">
            <img src="https://sample-videos.com/img/Sample-png-image-100kb.png">
</a>
<a data-fancybox="gallery" href="https://sample-videos.com/gif/1.gif" data-type="iframe" data-preload="false">
            <img src="https://sample-videos.com/gif/3.gif">
</a>

<script>
        Fancybox.bind("[data-fancybox]", { });
</script>