Ok, That means it might be google earned for that but not paying to the publishers.And some times , it will show like that for many publishers.
do not try to miss guide others.. eCPM is estimated earnings per every 1000 impressions, Adsense was trying to tell you that if you get 1000 impressions instead on 4 than your earnings would be $0.81, and for your kind information adsense doesn't show earnings less then $0.01 , In short you have earned less then $0.01 for 4 impressions...!