He was the only one to escape with his life, because he etherwalked.
We don't know if the MC was the only one to survive. Given how frequently some of the women at the park show up in his dreams, we can perhaps reasonably presume they can be any number of things, three of the most likely being:
- Memories from the mind of the MC, though why them and not, say, an ex-girlfriend or a friend?
- Echoes of the person
- Similarly trapped to the MC and the dreams cross-connect at just the right time.
Although that does make me wonder something. Given how the MC can travel to his home world for a brief time, why hasn't he tried to find out what happened in the park that day. Was it an explosion? An experiment that went awry? Even a cover up story from the government would be something.