You're suggesting he didn't?

It was a defect with the car
The park etc could a bit difficult to get it in. Making sure your car is in park is somthing people should do.

Anton was16d0 clean. It was a defect with the car; what a horrible twist of fate.
Poor guy.
"Don't get chumpatized!" - The King of Kong: A Fistful of Quarters (2007)

Actually, according to this, the last time the Hammerheads performed was June 11, just over a week before his accident
https://www.reverbnation.com/thehammerheadsmidnightcrusaders
Anyway, he should still be here today.
Yes he should and it sucks

The Hammerheads hadn't played in a few years and it sounded like they were done. It wouldn't be surprising if the meeting involved Anton's directorial debut "Travis" which would have started filming about two months after the events of that horrific night or that the 'meeting' was just 'spin' to describe he was gathering with a few friends to enjoy a Saturday night out on the town.
Anyway, he should still be here today.

The meeting was scheduled for 11pm (they found him around 1am) and I'm pretty sure it was a rehearsal for his band, The Hammerheads

Sorry. A professional meeting at 1AM? Look, I've worked in the film and theater industries and sure, hours are sometimes bizarre. But a rehearsal at 1AM? Yeah. Um. Not very likely.
We may never know the exact reasons for his meeting. But they wouldn't in any way diminish the tragedy.
He was a marvelous actor. And he became very hot once he filled out.

He was on his way to a professional meeting; it's unlikely he was intoxicated. Jeep is being investigated for just such a mechanical problem, the transmission shifting from Park to Neutral without cause.

dude he was clean,chill.