Trump is once again showing his complete lack of regard for the truth. He is claiming that the audience for his first State of the Union speech was the "highest in history". That is just more of his alternate facts, and not representative of the real facts.
The chart above shows the Nielsen ratings for the first State of the Union speech by Clinton, Bush, Obama, and Trump. Note that he had the smallest audience of any of these four presidents -- 200,000 less than Clinton, 6,200,000 less than Bush, and 2,400,000 less than Obama.
Even in his last year's speech to Congress (which was not really a State of the Union since he had just taken office) he finished third to Clinton and Obama -- beating only the first speech of Bush.
This is reminiscent of his claims about having the largest inauguration crowd in history, when government photos show that was not even close to the truth. He also claimed to have the largest electoral college win, but history shows us that several presidents have had larger victories.
Trump is a narcissist, and his narcissism demands that he be first (or best) in everything. Unfortunately for him, the facts have never come up to his ludicrous claims and wishes.