Why is it abnormal to remember the day of the week of something that happened? Particularly if this was the “last week” of the show (it wasn’t but it was near the end and he’s been quoted as saying he was on the last week of Oprah before enough to have a fact check on it: newsweek.com/fact-check…)
He even says a few sentences later “In that last - that final week” essentially repeating his first sentence “Last week”. It seems incredibly unlikely that he would both believe this interview took place last week, and immediately state that his interview was in the final week while having dementia. The far more likely explanation is that he was using an ellipsis, leaving out “the” at the beginning of a sentence.
You are entitled to your opinion on this, but you’re wrong.