What do HG and NA mean in Geuvadis project RNAseq sample labels?
If you google HG00105, among the first hits is geo accession GSM649517 with the title HG00105/NA12878.

Channel1:

Characteristics gender: Male
cell line: lymphoblast cell line HG00105
ethnicity: British from England and Scotland, UK (1000 Genomes codes: GBR)


Channel2:

gender: female
cell line: lymphoblast cell line NA12878
ethnicity: Northwest European American from Utah (HapMap code: CEU)


So no, they are not coding for the ethnic background but are part of the unique identifier of the sample.