Both naʿt (attributive adjective) and ḥāl characterize a noun, but they do so differently. In رَأَيْتُ رَجُلًا كَرِيمًا, karīman is an attributive adjective. In رَأَيْتُ الرَّجُلَ مُبْتَسِمًا, mubtasiman is an accusative circumstance describing the man's state when seen.
An attribute helps identify or describe its noun; a circumstance primarily specifies the state accompanying an action. Neither relation automatically demands an independent conjunction.