About 10 years ago, I was flying to visit family at the age of 15-16, on my own. My aunt dropped me off curbside at SFO, and I got a very similar phrase and tip suggestion from the attendant there.

Being that age I gave her $5 not knowing better, and to be honest felt like I was possibly being taken advantage of...but later on I learned that is in fact standard, although the way they ask does make you quite leery of the interaction as a whole.