Looks like the distortion is consistent across all harmonics.
https//pdfs.semanticscholar.org/9a52/fcba6dd87371974b3c146dbb5a3a00ffee74.pdf
These students were sponsored by NAIM to investigate ways to reduce this non-linearity harmonic distortion that is inherent to R-2R designs.
The 2nd harmonic will give this kind of DAC a richer sound. The higher odd harmonics will tend give an R-2R a slightly harsh edgy sound in the treble. My guess is that R-2R DAC manufacturers will use filtering to roll off the highs in order to reduce the odd harmonic harshness in the upper treble. Subjectively this might be preferable to a higher performance DS DAC.