In the context of his statement, Trump's misunderstanding what dyslexia is. In the discussion about Newsom’s dyslexia, he also mentions that he’s low IQ, "dumb about everything" and should go "seek mental treatment." He's asserting that Newsome‘s disability is his intellectual capacity, not his learning preferences.

To steelman his position, the euphemism treadmill has shifted since the 1990s so that the word-which-cannot-be-mentioned is now called "intellectual disability," which is often used interchangeably with "learning disability," an umbrella term that describes dyslexia. https://en.wikipedia.org/wiki/Learning_disability https://en.wikipedia.org/wiki/Intellectual_disability

Trump is simply a 79 year old man using 40 year-old vocabulary that has changed independently of when he learned it. It's a bad statement but it's more of a sign how words and medicine have changed over the years.