You're wrong because;

A) pg was simply pointing out what the guy had failed to mention in his post.

B) The manner in which you leave a partner to pursue your own thing can vary. It wasn't that he left, from pg's comment I get a feeling the issue is HOW the founder ended his affairs with YC and co-founder.

So relax, keep your side projects. all though I highly recommend that you focus one at a time. put all you can in one idea before you leave and potentially put your team mates in jeopardy to pursue another.