If this guy really wanted to defect he would have flown to China and walked across the border there where it is much easier than trying to cross the DMZ.  I think it is more likely that this is just some confused or mentally challenged old guy or someone looking for attention:

South Korean police have arrested a U.S. citizen who allegedly entered a restricted border area near North Korea without permission.

A 58-year-old man from Louisiana identified only as “A” was detained Monday after crossing the Civilian Control Line near the heavily fortified frontier, according to South Korea’s defense ministry.

People must have a permit to enter the area, which is just south of the Demilitarized Zone, a 2.2-mile wide, 150-mile-long no man’s land that divides the peninsula. It’s also the site of several tourist attractions.

Military officials initially said they believed the man traveled to South Korea planning to enter the North for political purposes. But investigators, who have turned the case over to local police, later said they had determined he had no communist connections.  [Stars & Stripes]

You can read more at the link.