I thought I had answered this elsewhere before, but can’t find that response at the moment. I’m not sure how the iaWriter fonts are packaged, but there is something about them that does not allow iOS to properly identify the variants in the family.
Drafts uses system methods to work with fonts. The iOS picker is used to select font family, and UIFont/NSAttributedString methods to render the fonts. If the “bold” variant is showing up, then it’s because iOS thinks that is the regular variant for that font.
Not much I can do about that. I don’t know much about the mechanics of how fonts are packaged and the variants identified under the hood - most font families seem to work fine, but some do not. I tried in the past to have some additional logic in there to work around these issues by doing hacky things like trying to read the font names and look for words like “bold”, “heavy”, but it was wonky and not very accurate.