It does not mean that you give the outward appearance of being humble in any way.
It is defined in the article as "an awareness that one’s beliefs may be wrong" and "intellectually humble people can have strong beliefs, but recognize their fallibility and are willing to be proven wrong on matters large and small."
This was tested with a study in which "participants read essays arguing for and against religion, and were then asked about each author’s personality", and evidence that "people who displayed intellectual humility also did a better job evaluating the quality of evidence."
There is a distinction between an individual's internal mental processes (as tested in this study) and the way they present themselves externally. Being outwardly assertive and confident absolutely wins elections and grants, but this is not at odds with an ability to internally re-evaluate one's beliefs.
I particularly enjoy this quote from the article, as it reveals that the authors may have missed a subtlety:
“If you’re sitting around a table at a meeting and the boss is very low in intellectual humility, he or she isn’t going to listen to other people’s suggestions,” Leary said. “Yet we know that good leadership requires broadness of perspective and taking as many perspectives into account as possible.”
I absolutely agree that good leadership requires broadness of perspective, but this does not imply that every suggestion should get an audience at meetings -- capable leaders often have a much broader range of experience than their reports, and dismiss suggestions not out of arrogance or closed-mindedness, but simply because they have already evaluated and discounted that path, and have elected not to spend their limited time bringing everyone else up to speed. (Which can have its own issues, but that's a digression.)