They're probably more limited by bandwidth than requests per second, but anyway you look the number of requests are still impressive considered the budget.

BTW, the site is not just fast: they serve images on high quality (same as the original [1], that can be multiple MBs per page [2]) at an pretty impressive speed too.

[1]: before someone asks why they don't optimize the images, this is by design since they want to serve high quality images. There is an optional toggle to reduce the image size, but this is disabled by default.

[2]: for those not familiar, the average number of pages on a manga is something like ~20, and this can be read in ~5 minutes depending on the density of the text. So you can easily consume 50MB+ per chapter.