Vu Gia Po was arrested after being discovered wandering on foot without any identification in the town of Athmuqam, which lies on the Line of Control, police official Yasin Abbasi said.
A Vietnamese government spokesman in Hanoi said Po was detained "around October 2013".
Pakistani officials were initially clueless about who he was and where had had come from.
"He looked Chinese or Japanese but could not speak any local language, he had no travel documents, no identification, nothing," Abbasi told AFP.
Po was detained for several months and questioned by various government agencies before being handed over to police. During that time it was unclear what authorities did to ascertain his identity.
Months later, local administration officials succeeded in identifying his nationality by showing him the flags and currency of a number of east Asian countries.