Leica licenses an optical design to Panasonic for the m4/3 format and other cameras. They are not manufactured by Leica. The lenses give a “Leica look” to the images. Mechanical design and manufacturing tolerances may or may not be similar. Panasonic ( and Olympus ) use engineered polymers for most of their lenses to save on weight.
A Leica lens is not the same as a Panasonic-Leica lens. Both will take excellent pictures though.
Leica also has a similar approach on some of their camera bodies which were licensed to Leica by Panasonic.