أَقْبَلَ الطُّلَّابُ يَبْحَثُونَ عَنِ الْمَرَاجِعِ.
The students arrived while searching for reference works.
“Yabḥathūna” is an affirmative imperfect verb; its plural subject suffix refers to the students. The whole verbal clause describes their state as they approached and functions circumstantially. It is introduced without a separate circumstantial wāw, which matches the rule for this kind of affirmative imperfect clause.
The wāw within the plural verb ending is not a coordinating or circumstantial particle. Confusing a verb's morphological component with a clause-linking particle would misidentify the grammatical structure.