778 is a homonym for eating.
Popular science, in the dialects around Jiangsu, Zhejiang and Shanghai, midnight snack is called "midnight snack", and 7788 means eating.
Extended data:
Word source
It comes from Tik Tok, a very popular person. Every time he makes a video of himself eating, he will say "Let's have some supper", and then the tone is very funny. It sounds like I ate something late at night, so 778 is on fire, which means eat.
Citation example
Hungry in the middle of the night, cook some noodles.
Reference materials? Baidu encyclopedia -778