It's not nonsense, but then I'm brainwashed of course... I want to stress that I don't think this makes Scottish school application panels racist, consciously or otherwise, but it is a simple truth that if a particular factor has nothing to do with ability to do a job then that should show up in the figures as a workforce statistically equivalent to the diversity of the population. Any difference and that means that there is still a connection between, say, your gender and your chances of getting a job. Whatever that connection is, simply ignoring it and you risk the problem persisting -- and, in particular, you actually risk missing out on people who are just as talented getting the job. Which is precisely the problem people want to avoid.
In this particular case, no BME headteachers ought to be compared with an expected number of about 15 based on current diversity of 5% BME, and then the number of BME people in Scotland was only 2% in 2001, ie about 7 BME headteachers instead. Given that the role of headteacher tends to require a great deal of experience, it's possible that this simply represents the lag between ending (or acknowledging, and tackling) discrimination and the population catching up; perhaps there is a case to be made that we shouldn't therefore be overly concerned yet. But in an ideal society, where there is no discrimination and only talent matters, then it does indeed follow that you should expect the workforce to be as diverse as the population. And, if it is not, then you should try to find out why.