You can still make a reasonable assumption even without contact tracing of this kind. 1. We have people getting infected with covid after provable close contac

You can still make a reasonable assumption even without contact tracing of this kind. 1. We have people getting infected with covid after provable close contact with others that are infected. 2. We have comparably few infections at outside events when people are standing close to each other, but it does happen. Even if you have no contact tracing for the walk-by infection case, just by looking at numbers 1 and 2 you could extrapolate to non-close contact outdoors not being very infectious. Or reasoning from another perspective, if walk-by were enough to infect people, everyone would have already had it.