  We revisit the short-time dynamics of 2D Ising model with three spin
interactions in one direction and estimate the critical exponents $z,$
$\theta,$ $\beta$ and $\nu$. Taking properly into account the symmetry of the
Hamiltonian we obtain results completely different from those obtained by Wang
et al.. For the dynamic exponent $z$ our result coincides with that of the
4-state Potts model in two dimensions. In addition, results for the static
exponents $\nu$ and $\beta$ agree with previous estimates obtained from finite
size scaling combined with conformal invariance. Finally, for the new dynamic
exponent $\theta$ we find a negative and close to zero value, a result also
expected for the 4-state Potts model according to Okano et al.
