The outside risk of catching covid (or any other airborne virus, for that matter) is significantly lower than the indoor risk, but it’s still non-zero, particularly in crowded areas. And depending on what type of masks people were wearing, they would have varying degrees of protection indoors.
So I don’t think it’s accurate to assume that the only ones who caught covid at OSH were indoors and unmasked. But I do assume a degree of complacency was a common factor in all of them, since complacency affects everyone.