Yeah, I don't think there's any doubt that he reached Ban-Kai...
Though I'm not sure about his clothes changing... For sure they seem different to me, but I don't think it really has anything to do with he reaching ban kai or not... Up until now, the Shinigami clothes have never been considered as a measurement of Shinigami's power... not like the soul slayers "Wow that's a huge soul slayer, he should have a huge amount of spiritual power"
And he said it in the beginning of his training, something along the lines of "I'm just a couple of hours away from reaching my ban kai"... so it's not surprising he's leaving already...