What does Metahuman's DNA file actually provide for expression mapping?

hi guys,
As I download my customized metahuman from MHC and open it in UE, I noticed that a “DNA Asset” is attached to the Face Mesh.

Through limited doc, I figured out that MHC is based on a large cloud database, each adjustment of character’s face is actually a reference from the database. Therefore I guess that the DNA file contains the mapping information, such as expression mapping, between character and the database.

However recently I found a video that shows openning a metahuman inside MAYA, modifying the mesh and then REGENERATE a DNA file, without further explanation of the methodology.
This video makes me confused: if DNA file contains indexing to database, then how can any customized modification in MAYA make sense for such a reference-based system? How did these indexing REGENERATED without a corresponding sample in dictionary?

Or did I misunderstand the actual meaning of DNA file?