It's a day commemorating orders that all enslaved people in Texas were to be freed, as I understand it. At that time, Texas was the last state to have slaves emancipated.
He's countering narratives. If you give a jackass enough rope, he'll hang himself. In this case, the jackass is being violent and trying to spin up traitorous enclaves across the country. Trump knows actions speak louder than words and he's not giving the media ammunition.
I don't like the capitulations either, but it's a good strategic move on his part.