I did a little digging into DoorDash's pay scheme, and from what it sounds, larger orders might carry a higher delivery premium paid to the driver, plus incentives, plus the tip. They are paid as follows: Base Pay + Tip + Promotions. Base pay is anywhere from $2-$10 based on time, distance, and deliverability. Tip is 100% to the driver for the delivery. Incentive includes peak pay, guaranteed earnings, and challenges.
So the least the delivery driver would have earned was $7.00 for the delivery ($2.00 service plus the $5.00 tip). If it was peak they could have earned $1-$3 more if you make 5 deliveries with an acceptance rate of 60%. So the driver could've made up to an additional $3.00 if he met this criteria.
I personally don't believe DoorDash has a really great payout model, it heavily pays the company over the delivery driver. If anything the driver shouldn't have a beef with the customer; they should have issue with DoorDash for their pay model. Honestly I wonder why the restaurant didn't have a delivery service of their own; those that serve pizza almost always employ delivery drivers.
As far as tip culture is concerned, I am personally not a fan even though I live in the U.S. but we have to live with it. There are scales used as guidelines for properly tipping service, and we use them. That said, 25% is a generous tip for a driver...they drove the food there. They didn't seat the customer, take their order, cook the food, serve it, serve drinks, clean the table, etc.