This post says that Craigslist uses "a chunk of bloated JavaScript to render something as simple as a collection of images" without describing the bloat or even saying how big it is. Then it offers an alternative solution that is actually more bloated because it loads all full-sized images that are in a gallery. Craigslist will only load full-sized images once the user starts interacting with the gallery, but also offers much smaller thumbnails first. The lack of thumbnails on the author's version also makes it harder to navigate since you have to scroll through each image to see it rather than just seeing the thumbnails below
You are correct. I have updated the article to mention the almost 400kB JS used for the image gallery rendering. Also updated are the inclusion of interactive thumbnails and better UX wording to help users understand that the elements are "scroll-able".