It’s called an Ellipsis and is a well known occurrence in spoken English.

Looking up the show he was referencing: 7th of February 2011, which was a Monday. I guess he didn’t correctly remember the day of the week from his interview a decade before.

No one “lacks” the ability to articulate definite articles when they ask “Heading out to lunch?” or “Want some coffee?” Ellipsis’ are probably used by everyone who speaks English dozens of times a day without even realizing it. To point to the use of one as evidence that he is dementia ridden is by far the least charitable interpretation of the facts one can have.

Is it more likely Trump was using a common turn of speech, or that he literally believed this interview happened last week and just so happened to mention how it was the last week of her show in the following sentences? You be the judge.