When he said they were “fixing to leave” take a step back instead of escalating the situation more.
Except that's not what happened...until he had told the officers 3x to "get out of my face".
In fact, the very first thing he said to them when they approached is "GET OUT OF MY FACE!"
The band director, in other words, signaled he wasn't going to comply with the cops.
Right away.
They had zero reason to have any confidence in anything the guy said afterwards.
This is like when the cops show up at the spot we'd be skating and I tell them "Get out of my face" several times, then tell them I'm taking a few more tries and then we'll leave. Yeah, right.
Again, would you have behaved differently than the band director and why/why not?