While not a legal defense, I think that Trump is acknowledging a kernel of psychological truth, in that all of his mistatements are not lies. Two years ago I wrote about how his ADHD (and narcissism) contribute to three different categories of untruths, all of which the mainstream media labeled "lies". https://dockruse.medium.com/reflective-lies-reflexive-lies-and-simple-falsehoods-a283ef2787bf

Some of his untruths are intentional attempts to deceive (reflective lies); some are just him spouting whatever comes to mind, without much consideration or filtering (simple falsehoods); and some are part of his innate response to deny/deflect (reflexive lies). Although they are all untrue, we shouldn't treat all of his false statements the same way.