That piece of roundabout is mapped as sidewalk=none, hence StreetComplete's question. In reality you can walk from the North side in via Draycott Avenue, anticlockwise over a traffic island across Nash Way and down to the supermarket.

I've previously mapped that sort of thing as having a sidewalk on the outside of the roundabout, as I figured it would serve the same purpose in terms of routing but I don't know what the official line is.