  The speed of growth for a particular stochastic growth model introduced by
Borodin and Ferrari in [Comm. Math. Phys. 325 (2014), 603-684], which belongs
to the KPZ anisotropic universality class, was computed using multi-time
correlations. The model was recently generalized by Toninelli in
[arXiv:1503.05339] and for this generalization the stationary measure is known
but the time correlations are unknown. In this note, we obtain algebraic and
combinatorial proofs for the expression of the speed of growth from the
prescribed dynamics.
