Conversion mechanics

Hi all - Inquisitor has a skill called “Flames of Ignaffar,” which has a conversion option called “Tainted Flame.” The conversion is from 100% Fire to Chaos and 100% lightning to Vitality. However, this skill base does not seem to do lightning damage at all (only later in the skill path), so why the conversion from lightning?

Do conversions attached to skills affect global damage sources - so any source of lightning, in this case, would be converted, or only damage sources from the base skill get converted?