A friend/relative in the country of origin or who the immigrant is going to?
Since the immigrant had to put down the name of some person here that would vouch for him, they had to put down something. In some cases, it was a banker or agent that had made the travel connections, not a relative.
Do a search and see if others also list Rosenbaum as the person they are going to. Look at the address of Rosenbaum and see if it's a commercial building.... and do a search for that address on Google to see if other immigrants listed it.