GoogleComputeEngineTemplateOptions.assignExternalIp defualt is true.
Disable "Assign Public IP" in the UI does not remove the option

My suggestion add to the code in JCloudsSlaveTemplate.java line 544

options.as(GoogleComputeEngineTemplateOptions.class).assignExternalIp(assignPublicIp);

if (options instanceof GoogleComputeEngineTemplateOptions) {
{{ // Always use our own credentials and let creation fail}}
{{ // if no keys are provided.}}
{{ options.as(GoogleComputeEngineTemplateOptions.class).autoCreateKeyPair(false);}}
{{ options.as(GoogleComputeEngineTemplateOptions.class).preemptible(isPreemptible);}}
{{ options.as(GoogleComputeEngineTemplateOptions.class).assignExternalIp(assignPublicIp);}}
}