The operative wording is "where social distancing is not possible."
From that wording, my guess is BOTH indoors and outdoors...
Sure, but outdoors even if you aren’t 6 feet apart, it still doesn’t seem to spread very well. For instance, children at a playground. There’s no evidence supporting the idea that they’re transmitting this virus in that situation, but kids run around and bump into one another at playgrounds because that’s what kids do. Especially the little guys (under 10) aren’t going to keep 6 feet apart from each other, but it doesn’t really matter. There’s zero scientific backing for masks in that situation.