Original: The NHC continued to overestimate how quickly Zeta would dissipate and early on January 5 they operationally downgraded Zeta to a depression, which was later confirmed to have been an error.
Simplified: The NHC still continued to overestimate how fast Zeta would dissipate and early on January 5 they actually downgraded Zeta to a depression, which was later confirmed to have been wrong.