happened to be 的意思是“碰巧是或在……”。

station-Atlantic Avenue-which happened to be the place where I had to get off.
车站—大西洋大道—恰好是我必须下车的地方

又如：

She happened to be there yesterday too. 她昨天恰巧也在那里。

She happened to be out when he called. 他打电话时，她恰巧不在家。