TalkinPeace2 - to be fair the article doesn't make a specific claim about a failed primary school head inspecting a secondary school, it says someone was concerned when they saw "an Ofsted report for a large secondary school which he believed had been written by an inspector with only primary school experience", and then there is a separate point that says "The BBC is aware of two former headteachers who were forced out because their schools were failing currently working as Ofsted inspectors."
The headlines are making it sound a bit like all inspectors are dragged in off the streets, when the articles explain in more depth about the former practice of using "lay inspectors" to give a wider assessment of schools in areas like safeguarding, care guidance and support, and so on. Lay inspectors aren't actively employed by the Inspection Service Providers anymore but they still have some on the books from back when this was how inspections were done - and who would have numerous years of experience in conducting inspections and who have been through the ongoing inspector training, however detailed that is - I'm not claiming it would get them to a point where they would necessarily be competent to judge a full range of teaching, but in fairness it is a bit more than dragging in any old school secretary or governor and giving them a clipboard and an evidence form as some commenters on the newspaper articles seem to think.
I think this would be a good chance to take a look at the continuing drive to outsource every possible scrap of government and local authority activity. The fact is that very few inspectors are employed directly by Ofsted anymore, only the HMIs. All these additional inspectors are working for commercial organisations who have £££ and shareholders/balance sheets are the forefront of their organisational minds - is that the best way to run a system of inspection?