The readme of this plus says the default of cloud parameter is "kubernets"
"cloud: The name of the cloud as defined in Jenkins settings. Defaults to kubernetes."

However, the plugin describes

"The Kubernetes cloud to use to schedule the pod.  If unset, the first available Kubernetes cloud will be used."

https://github.com/jenkinsci/kubernetes-plugin/blob/master/src/main/resources/org/csanchez/jenkins/plugins/kubernetes/pipeline/PodTemplateStep/help-cloud.html

In fact, the plugin chooses the first cloud if "cloud" is unset.