It doesn't matter if he was off-guard. Like they said it doesn't freeze you to the bone so Pizz could just break out and couldn't cause he wasn't built like that.
Doflamingo wasn't offguard + used DF so no comparison with DFless Pizarro getting caught offguard by Aokiji's DF power.
Aokiji isn't freezing Island Man Pizarro right now, he can literally control the island deeper ground, bedrock layer, he can't freeze that.