Of course Pres Trump was telling the truth.
The tweeter (Collin Rugg, who is a Trump supporter) worded it in his own way.
It was mocking the libertarians.
mock /ˈmɑːk/
to laugh at or make fun of (someone or something) especially by copying an action or a way of behaving or speaking
Perhaps “disrespected them”, or “was brutally honest with them”, would describe it better. It’s not a big deal either way, but I think “mocking them” conveys something different in most people’s minds, than what actually occurred.