An observable sensitive to the chiral magnetic wave (CMW) is the charge asymmetry dependence of the $pi^{-}$ and $pi^{+}$ anisotropic flow difference, $Delta v_{n}(A_{rm ch})$. We show that, due to non-flow correlations, the flow measurements by the Q-cumulant method using all charged particles as reference introduce a trivial linear term to $Delta v_{n}(A_{rm ch})$. The trivial slope contribution to the triangle flow difference $Delta v_{3}(A_{rm ch})$ can be negative if the non-flow is dominated by back-to-back pairs. This can explain the observed negative $Delta v_{3}(A_{rm ch})$ slope in the preliminary STAR data. We further find that the non-flow correlations give rise to additional backgrounds to the slope of $Delta v_{2}(A_{rm ch})$ from the competition among different pion sources and from the larger multiplicity dilution to $pi^{+}$ ($pi^{-}$) at positive (negative) $A_{rm ch}$.
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