He was enthused about his new camera when showing it to us.

was enthused 是动词 enthuse 的被动语态过去式形式。enthuse 由前缀 en-（表示"使进入某种状态"）和词根 thus（源自希腊语，表示"热情、激情"）组成，意思是"使充满热情"。was enthused 表示"被激发热情"或"表现出热情"的状态。