so this question - Candidates that are late for interviews? - is just a total mess.
It turns out that the OP's boss was to blame, giving a candidate a half hour block to attend an interview.
There is a great question there - is timeliness important for a job interview (and I suspect the answer is "it depends") but it's lost because, in this specific case, the answer is "oh trick question, they were never late at all".
Which isn't what the OP asked at all - I cannot think of a sane edit to be made to make this question useful to have around as it is. Because as it is, the actual question is closer to "when someone is late what things should one take into consideration to ascertain why they were late".