A quick internet search shows that this lowest crime rate was published in late April, early May. There's been a notable number of times that Trump has tweeted something that was the opposite of what everyone was saying yet was proven correct. If he's saying it, he's saying it either because he thinks it's untrue (a jab at police or news) OR he's trying to get a very specific reaction from someone. Either way, he's leading the news folks around by the nose. Yet again. And they never stop falling for it. It's free publicity for Trump and he gets a message out to cause something to happen.
100% if the news folks would stop covering Trump, he'd lose like 75% of the influence he has.
If you can't spot the bullshit... you're probably falling for it...