Engineers occasionally have conflicts of interest with their employers and clients (e.g. when asked to build something clearly dangerous) but it's very, very rare. And Engineers are almost never asked to conceal relevant information from people they directly work with..
Business people face conflicts of interest with their customers and suppliers every day.
In business? concealing relevant information is standard, in fact, you might be failing in your duty to your shareholders if you reveal relevant information to your customers or suppliers. But, you may be defrauding those customers or suppliers if you don't reveal enough information.
This makes business ethics a lot more complex. Now, I agree that the YC ethics as written are super vague and making them more clear would be very good. In fact, I think YC has a chance to set a standard here. Considering how YC explicitly asks for hustlers, and people who push the line, one could even argue that they have a responsibility to make the line clear.
However, it is an extremely difficult thing to do. When a task is beyond your means, is it better to put up a "better than nothing" attempt that doesn't completely solve the problem, or to put up nothing at all? I don't know.