I am not at all convinced that these knives are make by the Yao, not considering the rest of that material culture. This knife type doesn't fit anything produced natively in East Africa. I am not yet aware of any single-edged knife with this blade, bolster and partial tang construction anywhere in Africa.
This knife type does, fit into North Indian and Central Asian material culture. Considering the large Gujarati Indian Diaspora in East Africa, I can certainly see these knives being sold in Mozambique from an Indian source. I cannot, however, see these as being made by East African smiths, it's not within their style
I would say look carefully at the blade profile and section, the bolster assembly, and the tang connection. Then look into the very peculiar stamps, which appear to be standardized.
Emanuel