Not sure what "export control regulations" is this referring to. As far as I understand those only cover physical goods or encryption tech (in some jurisdictions). This is neither of those!
In fact, serving that error message would have probably been a violation of those regulations. Sending an error page is no different from sending the plugin (which is probably just a .jar with metadata).
In fact, Oracle had a similar geoblock a while ago but they quickly reverted it, for some reason