If you read footnote #2, the source images are 256x256 but downsampled using a VAE, and presumably upsampled using a VAE for publishing (IIRC they are less prone to the infamous GAN artifacts).
I know they use VQ-VAE under the transformer, but that would generate one symbol per 8x8 box. When you tile them up they should have some mosaic artifacts along the edges, if they generate these patches independently.
