Is Yungu unintentional an idiom?

No. According to the idiom dictionary, Yungu unintentionally is not an idiom. Yungu Unintentional is the work of Wu, a calligraphy seal engraver born in Shanghai. Wu Jitian is a famous young and middle-aged calligrapher and seal engraver. He is currently a member of China Xiling Printing Society, China Calligraphers Association and Shanghai Calligraphers Association, and vice chairman of Harmo Chinese Painting Working Committee of Shanghai Artists Association.