The BBC account of Cummings' actions, as quoted, just confuses matters. If I've understood this right, Cummings and Mrs C drive 260 miles London to Durham, stayed in a non relatives house on the off chance that they might be needed to free up relatives to look after children but his sister did the shopping and dropped it off so Mr and Mrs C weren't required to do anything so they drove back to London without having seen relatives or done the shopping but did stay up in Durham and Gove says that was "essential" and therefore OK. I think.
https://www.bbc.co.uk/news/uk-politics-52782913