BUT....I have never seen a small island like this in the States so

The NACTO minimum is 6', justified as "the length of a bicycle or a person pushing a stroller". PROWAG also has 6' min, don't know about prior ADA guidance. Per our local (LA) guidance smaller crossing islands are fine but shouldn't be treated as refuges

Do you have a streetview (or photo) example of a smaller island in LA?

Off the top of my head there's one or two narrow ones along Figueroa in Wilmington. LADOT has a vision zero dashboard where you can filter by project type. In general though I think the interpretation is that 6' is the practical minimum for new islands