Techs come from CIV4civilizationInfos.xml, unless the map overrides it.
UUs are basically overrides to the default unit class. In CIV4UnitClassInfos.xml there is a default unit foreach class set, so one gets this unless it is explicetly overriden. eg)
<Unit>
<UnitClassType>UNITCLASS_LIGHT_CAVALRY</UnitClassType>
<UnitType>NONE</UnitType>
</Unit>
<Unit>
<UnitClassType>UNITCLASS_MEDIUM_CAVALRY</UnitClassType>
<UnitType>UNIT_NUMIDIAN_CAVALRY</UnitType>
</Unit>
so this civ won't be able to build the unit in the light cavalry class, and when building medium cavalry they build numidian cavalry instead.