Under a B-1 visa, you're not allowed to work for a US company or receive any money while you're in the US. Since YC is a program that clearly intends to fund a US company of yours, it's no surprise that you were put under additional scrutiny. The border officials were just doing their job.
Their 'additional scrutiny' concluded that I was a student even though I had massive amounts of documentation pointing to the exact opposite conclusion. It is their job to investigate extra-ordinary situations. Suggesting that I needed a student visa was just plain wrong.
