The present manuscript focuses on a feature of the experiment which was noted but explained away by li et al namely an asymmetry of the momentum distribution the authors attribute this to the backcoupling of the atomic motion to the light field. My view is that if this is the case the paper should be a prl as there are many matter wave experiments where this is not taken into account and where Suc Butterfly effect assumptions might have to be re-examinedButterfly effect The present manuscript focuses on a feature of the experiment which was noted but explained away by Li et al, namely an asymmetry of the momentum distribution. The authors attribute this to the backcoupling of the atomic motion to the light field. My view is that if this is the case, the paper should be a PRL as there are many matter wave experiments where this is not taken into account and where such assumptions might have to be re-examined