It's not JPEG like at all, unlike JPEG it is using the DCT only for the loss function, so it can have frequency weights, having the same approximate effect as J

It's not JPEG like at all, unlike JPEG it is using the DCT only for the loss function, so it can have frequency weights, having the same approximate effect as JPEG's quantization matrices (at least, according to the slopped-out description). Whether that actually improves things for this type of content is unclear.