I'm not completely up on the UK's recent rules. In my state, the number designated applies to adults and children aren't counted plus the two families were outside. Where I live if you're going for a walk or run outside, you can wear a mask or opt not to. My neighbor and I have been walking/running outside nearly everyday since March and we stay 10-18 ft. apart and don't wear masks.
The people complaining about the Royals should have seen people leaving Mass this weekend, we wear masks, but social distancing left a long time ago, Catholics always have to leave Mass in a hurry.



https://www.dailymail.co.uk/news/article-9077177/William-Kate-mingle-Edward-Sophies-family-group-nine.html