In the following picture, you can see that in normal cells (yellow) we have two copies of each gene, while in tumor cells (violet), we just have one copy due to a clonal mono-allelic deletion. I do not really care about the genotype of the two genes, I just need to know that they are heterozygous.
On the other hand, suppose we are talking about somatic heterozygous SNVs and therefore we do not consider deletions anymore. In this case I would like to know the genotype (AA, AB or BB) of tumor and normal cells. Based on my understanding, I expect the AF of the SNVs in the tumor cells to be roughly 0.5 (since I ask for heterozygous SNVs). But what about normal cells? What is their genotype? If I ask for heterozygous SNVs, does that imply that normal cells are homozygous for that alleles?