Some initial thoughts that I had:
1) either the LDS Church is true or it isn't. If it isn't true, then nothing happens to a person's soul, right?
2) In LDS Church doctrine, even after a person is baptized posthumously, that person still needs to accept it.
3) My great-grandmother has been baptized posthumously at least three times, despite the fact she was baptized while she was alive (and a lifelong member at that). I use this to point out that some members of the Church tend to wildly put down names to be baptized for without doing their homework.
4 (and this is the big one)) I'm fairly certain that this is against Church policy to do Temple work for people who have next-of-kin who haven't given permission.
It was this last point that made me do some homework, so that I would present correct information.
And, low and behold, I found more information on the Chrusch's web site than I thought I would. While it was written specifically to talk about problems with baptizing of holocost victims, it applies here as well. I have copied the following from the Church's Newsroom section, and have put in bold some of the pertinent sections.
A fundamental Church doctrine is that God grants to everyone the opportunity to receive His offer of salvation. God’s offer is universal, but each person must choose for himself or herself whether to accept it — God does not dictate the choice and no one else can impose it. Church doctrine states that to accept God’s offer one must, among other things, have faith, repent of sins, and be baptized by immersion.
It is fundamental to the Church’s concept of God as perfectly just and perfectly merciful that the baptismal invitation be extended to all. The Church’s extensive missionary program is an effort to extend that invitation to people throughout the world. However, millions have died without the opportunity to accept baptism. Church doctrine teaches that these persons continue to exist in the afterlife as conscious spirits with the capacity to learn, exercise faith, and make choices pertaining to their personal salvation. Consistent with practices dating back to New Testament times (see 1 Corinthians 15:29), Church members perform proxy or vicarious baptisms on behalf of those who have died without baptism. Proxy baptisms are considered so sacred they are performed only in Church temples.
The temple (proxy) baptism ceremony is simple and brief. Two people, dressed in white clothing, enter a temple baptismal font. One offers a short prayer in which the name of a deceased person is reverently spoken. He then briefly immerses the other person in the water.
As required by Church doctrine, a temple baptism is noted on Church records. However, the Church does not list persons as members of the Church or “Mormons” merely because proxy baptisms have been performed. Church doctrine teaches that at some point the spirit of the deceased person will be informed that a baptism has been performed on his or her behalf and will be given the opportunity to accept or reject it. The Church has no way of knowing whether a person has accepted the baptism and thus does not consider such persons Church members. In this way, Church members extend the opportunity to accept the Church’s message and faith to all people.
Although the Church teaches that temple baptisms must eventually be performed for everyone who did not receive them in this life, from the beginning Church members have been taught to focus their efforts on their own relatives. Hundreds of thousands of members throughout the world conduct private genealogical research to determine the names of their departed relatives and then submit those names to temples for the performance of proxy baptisms. The process for submitting names is relatively open and depends on the accuracy and good-faith of Church members around the world. Because any Church member can research and submit names for temple baptisms, errors and duplications sometimes occur.
Church members are specifically instructed not to submit the names of persons not related to them. Before performing temple baptisms for a deceased family member born within the last 95 years, members are instructed to get permission from the person's closest living relative.
So, to sum it up: Yes, the person who submitted the name was in error.