If you want, explain it using equilibria. For simplicity, I will
use H+ instead of H3O+.
H2O H+ + OH- Reaction 1 (equilibrium reaction)
2K(s) + 2H+(aq) --> 2K+(aq) + H2(g). reaction 2 (forward
reaction)
This reaction will always go forward.
Since H+ is being consumed in reaction 2, concentration of H+ will
decrease. As such, by Le Chartelier's Principle, the system will
try to produce more H+ in reaction 1 so that the system reaches the
equilibrium, by shifting the equilibrium of reaction forward (to
the right) favouring production of H+ and OH-.