Why does Paul Hoffman refer to Jesus as "the guy in the womb of the whale"?

The conversation in the English version is pretty much identical to your translation;

“So it’s my fault? Well, if it is, I’m going to put it right. That boy is a menace. He’s a jinx like that fellow in the belly of the whale.”

“Jesus of Nazareth?”

“Yes, him. Once this business with the Redeemers is sorted, Cale is gone and that’s all there is to it.”

Note that in this instance, it's the two characters that are ignorant of Christian lore, not the author (or the translator).

Vipond and the Marshall are speaking together. The former vaguely recalls the tale of 'Jonah and the Whale' (from Jonah 1:17 - "Now the Lord provided a huge fish to swallow Jonah, and Jonah was in the belly of the fish three days and three nights") and the second character mis-identifies him as Jesus of Nazareth. Neither are evidently that well versed in bible lore.

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Jesus is also mis-identified as the 'whale guy" in the third book in the series (in this case by the narrator voicing Artemisia), lending credence to the idea that Jesus and Jonah have somehow been conflated into a single character in this universe.

It never came. Pushed underneath the ice by the current the oak tree began to roll—down it went like the Jesus whale, down to the bottom of the dam where a few hours before two great fangs of ice had formed.

_{^{The Beating of His Wings}}