People don't understand that admitting that you do not know does not mean you are dumb. It actually makes you dumb by not admitting it since you're wasting everyone's time by bullshitting and beating around the bush.
For an example of a subjective situation, in a poker game it can be useful to pretend to know you will win in cases where it is unknown, or even in cases where you know you have a weak hand. The other player's subjective impression of what you know is more important than its actual accuracy.
On the other hand, computer programmers and engineers usually are dealing with objective circumstances where not admitting you don't know results in things breaking and delays finding out the objectively true answer.
A common failing is to not recognize which of the two types of situations you are in, and just assume you should treat it like the one you are most used to. Hence engineering types may be ignored because they don't sound confident in their answers, and political types forget that that rules or legislation cannot override the laws of physics.
The better real world example isn't poker, but it comes up anytime you're talking with someone who knows less than you: your boss, customers, friends. The cost of being caught at wrong answers is often quite low.
And often the cost isn't only low to yourself, but to all parties involved. The article's author makes the leap to academic dishonesty right away. But, especially in this field of work, we talk a lot about the value of social skills over pure technical skills. BSing has a bad connotation but you can also think of it as consistently leaving good impressions or presenting things in the best light. It's not a rigid distinction.
A good example is the post below who said he probably got passed up for promotions because saying I don't know made the boss think he lacked "confidence". It's not surprising that the person in charge might disagree with the value of "I don't know". It's probably part of the social skill set that put him in charge in the first place.
Of course in the technical field the cost of a fudged truth can be very high, but the potential benefits are equally high, because you're often dealing with people who don't have the background to judge anything on its technical merits. The less knowledgeable they are, the more they have to rely on your presentation.
The "courage" to say I don't know is a good standard in academic and technical fields, but in the fields of business and politics (and social interactions in general!) it's not so clear-cut.