Large numbers of security troops check pilgrims, patrol the city, the man says following his first visit to the capital.
They say their opportunities to study Tibetan religious and cultural traditions were severely limited.
Police in Lithang pay frequent unannounced visits to Tibetan homes to search for photos of the exiled spiritual leader.
Namkha Jam had been jailed for sharing information and images of self-immolation protests with outside contacts.
But local Tibetans say the Chinese-run event was merely political propaganda.
Tenzin Choephel was taken into custody by police in late March and has not been heard from since.
Gonpo Tenzin was jailed for singing songs describing the hardships of life under Chinese rule.
The destruction follows similar campaigns carried out along the lake in the last several years.