Tbh that cook probably took it as a backhanded insult even though you meant it as a compliment. Grandmas chili is sacred to people, so saying some diner cook beat her recipe is like saying his food is better than his own mom's. He probably heard "your chili ain't special, my grandma's is just worse" instead of what you actually said. Next time just tell the cook it was good and leave grandma out of it.