5go,
There is one possible explanation for the "blooper". But before I talk about it, let me first say. I'm at work and don't have a Bible at hand and don't remember what the scripture says. But you said that Jesus remember the text correct but attributed it to Jeremiah. Well, I don't remember Jesus speaking of that prophecy. I think it was Matthew who wrote about it and attributed it to Jeremiah, not Jesus.
In any case, the explanation is that back then, the Prophets's writings were all put together and it seems that Jeremiah was listed as the first one because of the length of his writings. And it's possible that because of that, Matthew said it was Jeremiah and not Zechariah but obviously, it's not a mistake because back then, he could've just checked who wrote down the prophecy. Had it been a mistake or "blooper", I'm sure it would've been fixed long ago. There are other such "bloopers" where Jacob did something but it was attributed to Abraham, probably because Abraham was the head of the family.
As to the mention of a "unicorn", that has to do more with the translation than a Bible "blooper". Some Bibles don't translate it as "unicorn". There are animals mentioned in the Old Testament that we don't know what they looked like or what they were or that the Hebrew word for it is not easily translated. No one think unicorns exist or existed.
justahuman - but super nonetheless