Those people weren't included in the survey I don't think? The survey says it excludes anyone tested in care homes and hospitals and refers only to private household testing in the community. Maybe it's the school kids swaying the data but I don't know, you'd expect whole households to be infected anyway if their kids are.Health workers, care workers, school children too now, are all tested routinely regardless of symptoms.
Probably a lot of school kids in there.
Coronavirus (COVID-19) Infection Survey - Office for National Statistics
The characteristics of people testing positive for the coronavirus (COVID-19) from the COVID-19 Infection Survey. This survey is being delivered in partnership with the University of Oxford, the University of Manchester, Public Health England and Wellcome Trust.
www.ons.gov.uk