He also knows that government is not business. He's mentioned that a few times.
I won't Defend Trump attacking Sessions by the way. I think Trump could get similar ultimate effect without doing that. But I have to admit, there is all sorts of attention on the DoJ/FBI/Mueller relationship now, driven by the attack against Sessions. The spotlight is moving over in that direction.
But there are rules for managing an organization effectively and this kind of behavior would be damaging to any organization--business, government, or military.
If a man has something to say to another man, he says it to his face, not behind his back...and certainly not in public. Of course, Comey is the notable exception to this rule, but Comey was and is a skunk (no insult intended to actual skunks).
All that said, this is Trump, so who the hell knows what he's up to.;-)
Trump and Sessions have been friends for a long time and probably stay in very close contact. I have a hard time believing that Trump, who has a long history of manipulating the media, isn't just pulling another head fake here.