Why envoy behaves differently when envoy adds an error tag to trace according to HTTP and GRPC status?

*Description*:
Envoy adds an error tag to trace when HTTP status is 5xx (NOT when HTTP status is 4xx). On the other hand, envoy adds an error tag to trace when GRPC status is not "OK".

I think envoy should not adds an error tag to trace when GRPC status is such as "NOT_FOUND" or "PERMISSION_DENIED" because they are equivalent to HTTP status 4xx.

Is there any intention for this difference?

*Relevant Links*:
https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/observability/tracing#what-data-each-trace-contains