redis outlier detection when redis is down but Envoy is up

In the current implementation , when server Envoy is up but redis down, we send proper error response with "UpstreamFailure" - as a result of the this Client Envoy does not detect this as outlier and eject even when outlier detection is enabled on client side.

So in cases where redis container is down but Envoy is up - Should n't this failure treated as outlier from client side (similar to 503 in http)?

Or are there any reasons why this has been implemented like this?