There's also the fact that he's on the board of directors of Twitter while he's sending these text messages conspiring against the shareholders he represents!
He wanted to change the company in ways that he thought were better, but he couldn't get the support of the other stakeholders so he's leaving the board. He's discussing with a friend a combination of A) lessons learned and what he'd do differently if he could go back with his current knowledge and B) an abstract hypothetical that after he leaves the board maybe he'll work on a new project that does things better.
There is a huge difference between "I'm going to use my position at company X to harm company X" and "After I leave company X, I'd like to do a new project using the lessons I've learned".