You don't just get rid of the founder and CEO for shits and giggles. I'd love to know what it was that prompted this, although I'm not sure if we'll ever find out.
Since he doesn't claim to know why, by far the most likely reason is that they don't believe he has what it takes to take the company further, whether technically or in terms of management or industry experience.
Well he says he doesn't know why, but that seems disingenuous. If they had said they don't have confidence in his abilities to take the company forward that would be a reason - he could disagree but he would absolutely know why. So either they genuinely didn't tell him - which indicates it's something they think would cause trouble, or he does know why but won't tell us.
This is the cold hard world of business which is why founders should keep some decent equity to make sure they don't get stiffed like the guys at Fanduel: http://uk.businessinsider.com/fanduel-founders-likely-to-los...