Whether Chen Si Si's "Naxi Love Song" and Guo Zai's "Mongol Han" constitute plagiarism needs to be analyzed based on copyright law, comparing whether there is a direct similarity between the two songs in terms of melody, lyrics and other elements. If there is direct similarity, it may be considered suspected plagiarism. However, similarities in musical compositions can sometimes be just coincidental or common musical elements.
If you have questions about music copyright, it is advisable to consult a professional music copyright lawyer who can provide professional legal advice and services. It is very important to respect originality and comply with copyright laws in the process of music creation and distribution.