While for several reasons I do not think it is a good idea to use the same unsterile dropper on each persons finger, I am at the same time quite sure that no risk of HIV infection was involved as far you are concerned. To have a risk element involved the infected blood must enter INTO the body of the person concerned, merely a contamination on the finger is not of very great concern. I say this knowing that the puncture wound when taking a fingertip blood sample is extremely fine and seals almost immediately. If blood is still flowing out, the pressure will also prevent any return flow into the body. Please do not be concerned, that procedure did not put you at risk.