6 year old granddaughter's rudeness?

I am hoping for some reasonable advice. My son and daughter-in-law came over for dinner on December 30th. My granddaughter spat food she didn't like all over the table repeatly. My daughter-in-law tried to correct her and my son wouldn't allow it. Why is my son being such a jerk? I realize some people will bash me for this question. To those who help, I thank you in advance. (I never raised him like that.)