One thing not mentioned in wikipedia is that he made a White House petition to replace his Social Security Number, which failed with somewhere over 7,500 signatures (but not enough). Kafkaesque.
So we are assuming he was Mexican, moved to the US either staying at that address years ago or using it as a home address for records but not staying there. Worked as a travelling worker, somehow lost memory and either got lost or was abandoned by a group of others?
It's interesting to see how stories like these emerge during times of surveillance and tracking scare. I'm not trying to suggest dishonesty or paranoia anywhere, just pointing out how intriguing the dynamics of media stories are.