Do I have to tip when i pick up food?

I went to a restaurant to pick up food doing ‘curbside pick up’. I paid online and didn’t tip and when I got to the restaurant they brought the food out to my car. However, she asked me to sign my receipt. Even though I had already paid online and put 0 tip. Well, because of the pressure of her hovering over me and watching me sign, I gave a $5 tip 😭 it was 2 items and it cost $35 dollars. Would it have been rude to just put $0 for tip?