Any man can stand on the shoulders of the giants that came before them. A true goliath need not stand on them, for they already have their head resting upon the shoulders of a giant.
Long after the fall of the Titans, their kith and kin carried a fraction of their power. Some of them becoming known as giants, the giants themselves walking the Prime Material amongst the humanoids. And, just like almost every other sentient ancestry across the planes, a giant can't help who they fall in love with.
These children had the blood of the giants, but a weaker physicality and a more diminutive size (though still stronger and larger than other humanoids). These children were forced out by their fellow giant-kin, earning their ancestry the name for an exile in Küric.
While possible for there to be goliath of all kinds of giant, the most common kind of goliath are the kin of either Hill or Stone Giants. This is primarily due to the fact that Hill and Stone Giants are found in areas where humans tend to make their settlements.
Meanwhile Fire, Frost, and Storm Giants all live in the most extreme areas, where none but the most dedicated humans will even attempt to live.