The first chapter of the book of Daniel establishes that Daniel is not willing to ever eat choice food or drink wine. Daniel makes a big deal out of this. He has religious reasons for his dietary restrictions, as well as health reasons. He insists on eating nothing but vegetables and drinking nothing but water, even if doing so risks incurring the wrath of the king.
Later on, Daniel is writing about how troubled he was after he had a vision about a future war. He says he was so distressed that for three weeks, he didn’t eat any choice food, eat any meat, or drink any wine.
That sure doesn’t sound like something you would say if you never ate those things in the first place.
Maybe Daniel was just trying to sound dramatic by making the technically true statement that he had abstained from those things for three weeks, even though that wasn’t actually a change from his usual behavior.
Or maybe Daniel decided at some point that it was okay to defile himself by eating those things after all, and he had been risking the king’s wrath for nothing. And the authors didn’t think that change in Daniel’s beliefs was worth mentioning.