Pretty sure the "you're a liar" is just a convenient way to blow it off without going into details.

The buy was probably already questionable even for $50m, a number Steve probably already knew even before they entered the room. The exchange showed that the founders were going to be stubborn about the price.

So in the end this isn't "trust is everything in business, and Steve was offended" but simply "don't jump into negotiations with your pants down".