I have a question w.r.t connectivity to a GCP VM instance from on-prem machine.

This is the setup:

There is an MIG setup in GCP with no external address. The MIG has only internal address.
The MIG has a single machine (VM) inside. And it has only internal address.
SSH for both MIG as well as to the VM behind the MIG are disabled from GCP web console.

The weird thing is that: I am able to SSH into the VM from one of my on-premise machines (say: my laptop).

I don’t quite understand how this can happen when the VM does not even have an external IP assigned.