Oh, that's easy: "founder mode" means the founder is hyperfocused (or in the oldspeak, obsessed) on his work (with his company) and optimizes (micromanages) everything. We know that already. Perfection demands micromanagement. Steve Jobs was actually doing that - reaching down the ranks and directly helping (molesting) people doing some piece of a larger product he particularly cared about.

It also often causes (or is caused by) eccentric behavior (or mental issues) - but it's been done since forever, and when it's successful, we call it "visionary." When it's not, we call it "toxic."