Area striking question

I'd like some clarification of the Area Striking rule in melee.  Under the "Who Can Strike" section, the rulebook states:  "Models... may only strike at models from the target unit."  Then in the "Area Striking" section below it, the rulebook states, "models may split their attacks as evenly as possible between all enemy units within 3" of a single model."  Therefore, can models with multiple attacks strike any and all enemy units within 3" of their target, or can they only attack models from the same unit as their target?  Thank you for your consideration.