Can anyone explain me why plague doctor wasn't corrupted and said the truth? I thought corrupted characters can't do their jobs. That's what 'Corrupted' tag explains.
Yup, corrupted characters lie. Here Plague Doctor was not corrupted, so he told the truth.
Pooka only corrupts adjacent villagers. The Plague Doctor is an Outcast, not a Villager, so was not corrupted by Pooka.