In Fig. 5 on p. 311 of our Phys. Lett. B 740 (2015) 303 an adjustment by ${180}^{\circ }$ is required for the phases with respect to the $L=2,M=1$ wave, of the following waves: $L=1,3,5$ with $M=1$, and $L=2$ with $M=2$. After this correction (Fig. 5 (corrected) below), the extracted partial waves describe the angular distribution of the ${\eta }^{(\prime )}$ in the Gottfried-Jackson (GJ) frame, using Eq. (4) with implicit Condon-Shortley phase convention. The other results of our paper are not affected. The right-handed GJ coordinate system was defined by the z-axis pointing in the direction of the beam in the ${\eta }^{(\prime )}{\pi }^{-}$ center-of-mass system and the y-axis pointing in the direction of $p_{\text{recoil}}^{\text{GJ}}\times p_{\text{beam}}^{\text{GJ}}$.