كَوْنُ الْجُمْلَةِ الثَّانِيَةِ جَوَابًا عَنْ سُؤَالٍ نَشَأَ مِنَ الْجُمْلَةِ الْأُولَى
The second sentence answers a question naturally prompted by the first.
A listener hears the first statement and mentally asks a question that need not be spoken. The second sentence immediately answers it. Their relation resembles a question-and-answer exchange, so a conjunction is not required.
It is not complete connection, since the answer is not a mere restatement, nor complete disconnection, since there is a clear semantic link. Hence the name “resembling complete connection.”