Consider things from his perspective: during the development of the iPhone he was working on a tiny team and had complete ownership of an entire app. That is thoroughly start-up like.
In the original NYT article that is not even a direct quote from him, but the reporter's interpretation of what he said. Given that the article also indirectly reports him giving a "rare window into the companys start-up-like product development," the "no longer felt like a start-up" paraphrase makes perfect sense in context:
"Mr. Tolmasky said he left Apple in late 2007 because by then, the iPhone had become such a success that the team had to grow and priorities changed. It no longer felt like a start-up, so he left to start his own."
Clearly, he's someone who likes to own a project, not share it with a team of 10 or 20. He prefers broad-stroke inventing to focused work in a narrower niche. That kind of self-knowledge as a developer is the exact opposite of immature and weird. It's mature and wonderful and all too rare.
I am sure he is ten times as happy and productive doing what he does now as he would have been as one cog in the machine at Apple. And there are plenty of developers who prefer to have highly-focused expertise and responsibilities. I am sure one of them is being far more effective in his old job than he would have been.
The whole workforce wins when people are smart enough to put themselves in situations that play to their strengths.
