Here's a contemporary opinion, from the state attorney general at the time, the highest ranking person in a judicial apparatus that didn't prosecute anyone for participating in it. Looks like the fact that "the Negro" was so rich he didn't "accept the white man as his benefactor" was a pretty big deal...

The cause of this riot was not Tulsa. It might have happened anywhere for the Negro is not the same man he was thirty years ago when he was content to plod along his own road accepting the white man as his benefactor. But the years have passed and the Negro has been educated and the race papers have spread the thought of race equality.