Verb-vs-noun is the whole game here.
缝 (rising tone) is the verb 'to sew' —
缝衣服 (sew clothes),
缝合 (suture),
缝纫 (sewing). The same character read
缝 (falling tone) is the noun 'seam / crack / gap' —
门缝 (door gap),
裂缝 (crack). Verb → action → féng; noun → result → fèng.