Why is 4-hydroxypyridine more acidic than benzoic acid?
The following are two resonance forms of 4-pyridone,


So, when 4-pyridone gets de-protonated, the negative charge on nitrogen gets delocalised on more electronegative atom i.e., oxygen, resulting in more stable resonance structure!
Note that, this explanation is identical to that one which is given when we compare $\mathrm pK_{\mathrm a}$ of benzoic acid and phenol.

Ref: Stability of 4-pyridone vs 4-pyridinol