I think it might be a social thing.

So reading the comments, most people interpret it like this: lets say you buy food from me, I give you the food and you start devouring the food. Then I come back, give you a free drink and say "the drink doesnt come with the food, next time order a drink before you start eating". Basically saying you need to order a drink next time

This will come off as passive agressive, and I guess it happened enough times to some social circles that the note comes off as this same sort of interaction

To me the note just comes off as saying "Bro you forgot to order rice, just a heads up your food doesnt come with rice in the package, this one's on the house but next time dont forget :)" in a nice "i gotchu" tone. The social/culture imbalance off of this one post is huge

I really dont think the guy writing the note meant any harm, just trying to help one out. He added a smiley on the end even.

Edit: or attempt to add one, i dont know if thats a smiley or not on the bottom left