생각나다 is a thought arriving on its own, unlike 생각하다, which is thinking on purpose. Every line here is 뭔가 생각나다, 'something came to me' — 방금 뭔가 생각났어, 'I just remembered something'. It is a caption staple for the moment someone interrupts themselves: 갑자기 또 뭔가 생각난 차 씨.