This is typical Trump tactic -- divert attention away from some worsening scandal he's facing by making a totally preposterous claim that, in turn, spawns its own headline-devouring scandal.
It also turns the conversation to a discussion of his favorite topic -- himself. And he can play the victim card, too, at the same time. Not only have the bad Democrats fabricated a number, they did it to hurt him.
It also sends the message that any media outlet that doesn't report the "truth" about the number of victims cannot be trusted. You can only trust Trump and the few media outlets that report his claims as accepted truths.
What results is what some call a "first-degree lie," meaning a lie that was planned in advance of its utterance. It's the worst kind of lie because it shows a President who will stoop to any depth, no matter how low and shameful, in order to fluff his ego.