The plugin tries to automatically install Java on the agent when it is not found. https://github.com/jenkinsci/windows-slaves-plugin/blob/d7f0dd6a274456d2d2cc0fc6bd67aef5382bfae9/src/main/java/hudson/os/windows/ManagedWindowsServiceLauncher.java#L235

This code does not work for new Jenkins versions anyway, because Java 6 is no longer supported. But if it magically works and installs something, it will be a subject to usage and license constraints documented in https://github.com/jenkinsci/jdk-tool-plugin 

I suggest just removing the Java auto-install feature. If it is not possible, we should probably switch to https://github.com/jenkinsci/adoptopenjdk-plugin