  In two dimensional magnets, the interplay of thermal fluctuations and spin
anisotropy control the existence of long-range magnetic order. In the van der
Waals antiferromagnets FePX$_3$, orbital degeneracy in the $t_{2g}$ levels of
the Fe$^{2+}$ ions in octahedral coordination yields strong uniaxial
anisotropy, which stabilizes magnetic order up to $T \approx 100$ K. Recent
inelastic neutron scattering measurements around the magnetic ordering
transition have shown the existence of a broad spectrum of magnetic
fluctuations with nontrivial momentum dependence, what has been interpreted as
evidence for localized entangled cluster excitations. In this paper, we offer
an alternative interpretation using classical non-linear spin dynamics
simulations. We present stochastic Landau Lifshitz dynamics simulations that
reproduce the neutron scattering measurements of Chen et al. [1] on FePX$_3$.
These calculations faithfully explain the dynamical structure factor's momentum
and energy dependence and point to a classical origin for the excitations
observed in neutron spectroscopy and that the order-disorder transition can be
understood in terms of thermal fluctuations overcoming the anisotropy energy.
