Why are both warm and cold currents found at the same latitude?

Because the wind drives away warm surface water, and colder ones rise in their place.
One of the factors is the origin. Thermal waters give rise to a warm current; the places where such water comes to the surface does not depend on latitude. Another factor can be considered the wind, often the wind drives away warm currents, thereby freeing the cold deep waters. Therefore, within the limits of 1 parallel, there can be both warm and cold currents.