tips for roadside service

en, I really can not understand the ”小費潛規則“ in US.  This morning, our 2004 Honda Oddesey could not start, since the light inside was left on overnight undeliberately. My hu*****and's car is right beside it and we have a 3.8meter long jumping cable.  But he rushed out to his work and left me with a number for paid-service.  I called the number and a guy came in, hook the cable with his charger and I started the car.  Then he left after this 2min on site service.  Now I am leaving it run for 30 mins.

What puzzled me a bit at the end was that before he left, he talked with me "I am anticipating to get tip from you".  I paid more than $50 to let him drive to my home and jump the car, then I have to pay the tip as well? I probably should pay $5 as the 10% of the service, but he really just did hooking it up and that's it.  I should have just asked my neighbors (I was concerned if the cable is long enough).  Anyway, I paid him $3.  I was not happy now, because for the ”小費潛規則“, I should paid him more probably.  But I was shocked when is asked for tip face to face.  I think paying tip is a courtesy and handled with grace.

Would you please teach me more about roadside service "tip rules"?  Thanks!