Well, he said they drove to have a walk. He can have more than one reason for leaving the house and as a non-lawyer he wouldn't be expected to list them all (and was clearly confused between the guidance and law).
I am not saying he did or didn't have a 'reasonable excuse' but I don't think it's as clear cut as people are making out that he didn't. Appreciate I am in a minority (possibly of 1!) of lawyers on this site who say he is bang to rights
This is the government guidance at the time by the way (10 April) web.archive.org/web/2020041112… 
