Thanks for the response. The USCIS website actually now says that being in an accelerator is fine with a B1, and in fact if the accelerator has fixed start and end date that can act as a proof that I will return home after the accelerator ends. Look at http://www.uscis.gov/eir/visa-guide/b-1-business-visitor/und... under "How do I show that I intend to remain for a limited time?", it's the 3rd point.

Silly me, I didn't see that before the interview. Anyways, my interviewer was new and had no idea what an accelerator was.

What I am doing now is interviewing in another city, with the same application, albeit with added true information that would support why I want to come back, which I honestly do in the short term as my parents are unwell. The city I interviewed in first has almost no startups, so they have never encountered a situation like this before. This time I am interviewing in a city that has a history of sending startups to US accelerators including YC and Techstars.

Let's see, I am interviewing this week. Taking all documents including my parents medical documents and a printout of the page above. Fingers crossed!