Would you have been concerned and made a post if the man was NOT "middle eastern looking"? Are you implying that if it was a white man that boarded the wrong plane that would just be a mistake, but in this case it becomes a "security lapse"? Are you proposing that UA should ensure that "middle eastern looking" people are subject to extra checks of their documents?

Since, as others have already pointed out, he was screened and permitted into the sterile area like you and everyone else, what exactly is your concern?

Perhaps considering your responses to these questions may help provide you with the 'enlightenment' you seek.