The greatest difference between the two situations is that one event happened in front of you and you were able to witness it while the other case is an event that one will not personally witness. However, whether it be in responsibility or cause and effect wise, the results are the same. The excuse of not happening in front of me is too weak to say that the cases are morally different.
Keeping them alive is different from giving them a quality life that maximizes the giver's and sender's happiness. , so as a result it undermines Singer's Ultrarianism.