SSL: Full (Strict) does not verify Google Cloud Storage certificate

I have a CNAME to a GCS bucket, per Google’s static website docs.

Bucket name:

The subdomain is orange-clouded and I use SSL: Full (Strict) with no Page Rules. I believe this should produce an error 525 or 526, since Google’s servers are not serving a valid certificate for my domain, but it seems to work fine. Is this expected behavior? Is there an exception made for GCS? This setup is actually ideal for me, but I’m worried that it might break, since it seems to be undocumented.