Does Istio cache TLS credentials? or Istio client doesn't verify server certificate?

Networking
1

I configured a DestinationRule to use TLS. This is my DestinationRule:

apiVersion: networking.istio.io/v1beta1
kind: DestinationRule
...
spec:
  host: myhost.com
  trafficPolicy:
    portLevelSettings:
    - port:
        number: 8443
      tls:
        mode: SIMPLE
        credentialName: myhost-tls

At first, I had ca.crt, tls.crt, tls.key in the myhost-tls secret, and the connection worked. However, the connection still worked after I deleted the secret. Hence, I am wondering does Istio cache the TLS credentials or does the Istio client actually doesn’t verify the certificate sent from the server?