"Don't go outside, you'll get COVID", sounds more and more like horrible advice. Before knowing the virus died in sunlight, I still couldn't fathom why people were avoiding going out to parks and stuff. It was totally non sequitor.
The concern was presumably crowds at parks. Viruses take a while to die from sunlight; it's not going to save you from breathing in the droplets from someone standing right next to you. (Not to mention choke points like public bathrooms, or in places like NYC, residential elevators to get to them.)
The likelihood of people being crowded in a park is much lower though due to inherint lower density. All the parks I saw closed their choke points (bathrooms, water fountains, etc) so I feel like being outdoors in a park is still much safer than staying indoors, going to grocery stores for example. But people were acting as though you could get it by just going outside. There was/is alot of fear mongering around leaving your house at all.