Part of the explanation for your observation that many international students are excellent students is selective migration by bright ambitious individuals to the nation with some of the best universities in the world, especially our masters and doctoral programs. For generations America has been a magnet for those who perceived the U.S. as the land of opportunity.
My grandfather was the only one of his ten siblings to migrate to the U.S.A. After working for others for a few years, he started his own business and became a leader in his field.
As a young man a member of my family taught at a university overseas. He met and fell in love with a student there. After she graduated she immigrated (legally) to the U.S. and they were married shortly thereafter. She arrived with all of her worldly possessions in one standard size suitcase and one carry-on suitcase. I told her how brave and courageous she was to leave her family and friends and come alone to the U.S. on a one-way ticket.
Later she told me, "I have dreams", including the dream for more education.
In medicine sub-specialists can develop misperceptions due to referral bias. I remember a group of physicians in conversation with an infertility specialist who had the perception that oral contraceptives were a common cause of infertility. He said, "Most of the women I see for infertility had trouble getting pregnant after stopping birth control pills." Someone asked him if anyone referred him patients who had no trouble getting pregnant after stopping birth control pills.
Another example of referral bias: About 15 years ago an endocrinologist at a nearby prestigious medical school said that a recently introduced category (glitazones) of diabetes medicines appeared not to be very effective. Several of us who had a number of patients who were doing well on one of those new diabetes medicines were puzzled at his remark. When someone asked him why he thought this new category of diabetes medicines didn't work, he responded, "All of the patients I see who tried one of those medicines didn't do well." Someone told him that the patients who did well on one of those medicines did not need to be referred to him.
Selective migration and referral bias can lead to misperceptions.