My first sister recalled this incident happened in 2018 when she was in the U.S. to see her son. The boy was 20 years old going to college there.
At the end of the semester, my sister went to his college to fetch him back. The school was almost empty. My sister was excited to see her son but she could see that the boy didn't share her excitement in going home with her.
Indeed, he went straight from his college to K-State with his friend and didn't get back until after my sister asked him to.
Considering the fact that my sister had a high hope for spending more time with her son after traveling all the way from China, her disappointment must have been magnified by his choosing to spend some time with his friends away from his mother.
My sister has all the right to feel unappreciated and hurt. But she buried it all inside without saying anything at that time. Still she describes it vividly even today.
It's possible that the son was not mature enough to fully realize the impact his actions had on his mother and the significance of her visit. In this case, when facing immature adult child, I think parents should communicate their wishes clearly beforehand, like "I am coming over to see you. If you have other commitments, I can come over another time." Open communication between my sister and her son could make life easy for both.
I told my second sister who is going to Shanghai to see her son, "Ultimately parents need to realize and accept the fact that children have their own priorities in life. Children may want to spend time with their friends or their better half or doing something else which they consider more important than spending time with the parents."