Prior to this sentence, Kawashima was talking about jumping from the school's roof with Obata-sensei; aftwerwards, another teacher is speaking with Obata, and says:
I'm guessing the
不安になってらした means "became worried/uneasy", but I can't understand what's
じゃないか, so like asking "isn't it?" rather than denying? So the whole sentence sounds like "During the free study period you happened to hear Kawashima speaking, so you became worried, isn't it?".
I'm having quite some difficult following this story so I'm not sure: on one hand it sounds right, on the other Obata did hear Kawashima - Obata didn't just happened to hear, Kawashima was speaking directly with Obata. It could be a roundabout way to say Obata knows what Kawashima said, but I'm not sure.